MC LCPhng php nghin cu khoa hc................................................................................................. 1 Mc tiu:..................................................................................................................................... 1 Nghin cu khoa hc l g:......................................................................................................... 1 Cc c im ca mt nghin cu khoa hc tt......................................................................... 1 i cng v thng k v thng k m t....................................................................................... 3 Mt s nh ngha ........................................................................................................................ 3 Bin s v cc loi bin s .......................................................................................................... 3 Phng php m t tm tt v trnh by s liu .......................................................................... 3 Cc s thng k m t................................................................................................................. 4 Phng php trnh by s liu..................................................................................................... 6 i cng v phn tch s liu ...................................................................................................... 14 Suy lun thng k ...................................................................................................................... 15 Xc nh v chn u tin nghin cu ............................................................................................ 28 Mc tiu .................................................................................................................................... 28 Xc nh vn ......................................................................................................................... 28 Tiu chun chn u tin cho vn nghin cu....................................................................... 28 Thang im nh gi cc ch nghin cu ............................................................................ 29 Bng im................................................................................................................................. 30 Phng php phn tch v khng nh vn nghin cu ............................................................ 31 Mc tiu .................................................................................................................................... 31 Phn tch vn ........................................................................................................................ 31 Cc bc phn tch vn ................................................................................................... 31 Xc nh phm vi v trng tm ca nghin cu ........................................................................ 34 Xy dng phn t vn ......................................................................................................... 35 Cc thng tin cn thit trong phn t vn ........................................................................... 35 Tng quan y vn ............................................................................................................................ 36 Mc tiu................................................................................................................................... 36 Ti sao cn phi tham kho y vn khi chun b cng nghin cu ...................................... 36 Nhng ngun thng tin c th tham kho................................................................................. 36 Cch vit phn tng quan .......................................................................................................... 37 Sai lch c th........................................................................................................................... 37 Mc tiu nghin cu ...................................................................................................................... 39 Mc tiu hc tp:....................................................................................................................... 39 Mc tiu nghin cu l g: ........................................................................................................ 39 Ti sao phi xy dng mc tiu nghin cu .............................................................................. 39 Yu cu ca mc tiu nghin cu............................................................................................. 39 Gi thuyt nghin cu............................................................................................................... 40 Tn ti nghin cu ................................................................................................................ 40 Tho lun nhm......................................................................................................................... 40 Gii thiu v phng php nghin cu khoa hc y hc ................................................................ 41 iMc tiu .................................................................................................................................... 41 Gii thiu................................................................................................................................... 41 Bin s........................................................................................................................................... 43 Mc tiu .................................................................................................................................... 43 Bin s....................................................................................................................................... 43 Bin s nh tnh v bin s nh lng .................................................................................... 43 nh ngha c th ...................................................................................................................... 44 Bin s c lp - ph thuc - gy nhiu .................................................................................... 45 Kim sot yu t gy nhiu....................................................................................................... 45 Bin s nn (background variables) .......................................................................................... 46 Cc loi nghin cu....................................................................................................................... 50 Mc tiu .................................................................................................................................... 50 M u ...................................................................................................................................... 50 Mt s loi nghin cu .............................................................................................................. 50 Nghin cu khng can thip..................................................................................................... 50 Nghin cu can thip ................................................................................................................ 54 Tnh gi tr v tnh tin cy ca kt qu nghin cu................................................................... 55 Cc s o dch t hc .................................................................................................................... 56 I. M u: .................................................................................................................................. 56 II. S o tuyt i v s o tng i....................................................................................... 56 III. T s, t l, t sut................................................................................................................. 56 IV. S o dch t....................................................................................................................... 57 S o hu qu v s o tc ng................................................................................................... 59 I. Nhc li v s o s xut hin ca bnh: t sut, nguy c v s chnh................................. 59 II. S o s kt hp - s o hu qu .......................................................................................... 59 III. S o t s ............................................................................................................................ 59 IV. S o hiu s....................................................................................................................... 61 V. Bin lun thm v t s nguy c v hiu s nguy c ............................................................ 62 VI. S o tc ng..................................................................................................................... 63 VII. Bn lun thm v phn s nguy c quy trch dn s......................................................... 65 Phng php thu thp s liu ........................................................................................................ 66 S dng thng tin sn c........................................................................................................... 66 Quan st..................................................................................................................................... 66 Phng vn mt i mt v b cu hi t in........................................................................... 67 Thit k b cu hi .................................................................................................................... 67 Ly mu iu tra ............................................................................................................................ 71 Mc tiu:................................................................................................................................... 71 i cng v phng php ly mu: ........................................................................................ 71 Cc phng php ly mu xc sut: .......................................................................................... 72 Cch tnh c mu........................................................................................................................... 79 Mc tiu .................................................................................................................................... 79 Gii thiu................................................................................................................................... 79 iiHai cch tip cn trong tnh c mu .......................................................................................... 79 Cc im cn lu trong tnh c mu ...................................................................................... 81 Tnh c mu bng phn mm Epi Info:..................................................................................... 81 Th d ........................................................................................................................................ 83 Chin lc phn tch s liu .......................................................................................................... 84 Ci t chng trnh Stata 8.0 v s liu mu .............................................................................. 90 Khi ng v kt thc Stata......................................................................................................... 93 M t ngn gn v Stata ................................................................................................................ 97 Lnh more..................................................................................................................................... 99 Thng bo li v m phn hi..................................................................................................... 100 Phm break .................................................................................................................................. 102 S dng bn phm trong Stata..................................................................................................... 103 Khi ng Stata .......................................................................................................................... 105 1. Khi ng Stata................................................................................................................... 105 2. M t giao din ca chng trnh Stata .............................................................................. 105 3. Cch cch thc hin lnh trong chng trnh Stata ........................................................ 106 4.Lu li kt qu phn tch .................................................................................................... 106 M t s liu vi Stata 8.0 for Windows..................................................................................... 109 Thng k phn tch bin s nh lng vi Stata....................................................................... 143 Thc hnh ................................................................................................................................ 145 iiiPhng php nghin cu khoa hcMc tiu:- M t c cc c tnh ca mt nghin cu khoa hc- Trnh by c cc c tnh ca mt nghin cu khoa hc ttNghin cu khoa hc l g:Nghin cu l cng vic tm kim mt cch c h thng cc kin thc mi, da trn s t m v nhu cu c cm nhn.1Nh vy c im ca nghin cu ltm ra kin thc mi. C hai phng php chnh tm kim kinthc:hoclxem xtcctiliu, kin thcsnc tm ra cc kinthc mi (scholarship) haydavothctkhchquanpht hincckinthcvhiubit mi (scientific research). Phng php da vo thc t khch quan tm ti cc kin thc mi c gi l nghin cu khoa hc.2Nghin cu khoa hc l vic thu thp, phn tch v l gii s liu gii quyt mt vn hay tr li mt cu hi (Theo Varkevisser v cng s, 1991).Ni cch khc, nghin cu khoa hc phi bao gm cc bc thu thp s liu trn thc a (hay t cc ca bnh trong bnh vin hay phng th nghim), phn tch s liu c thng tin v v trnh by cc thng tin ny trong phn kt qu v trong phn bn lun v kin ngh, l gii cc thng tin tr li cho cu hi nghin cu hay xut cc bin php gii quyt vn .S liu: Kt qu ca vic thu thp c h thng cc i lng v c tnh ca cc i tngThng tin: S liu c phn tchKin thc: thng tin c l gii v c s dng tr li cu hi hay gii quyt mt vn no Nhng qu trnh thu thp, phn tch v l gii s liu din ra tt p v gii quyt c vn nghin cu, trc nh nghin cu phi phn tch t vn , xem nhng kin thc g bit v cn cha bit v vn . Qu trnh ny c gi l t vn , tng quan y vn. Sau nh nghin cu phi xc nh hi c c kin thc cn cha bit , cn nhng thng tin g v c nhng thng tin ny cn thu thp nhng i lng v tnh cht no ca i tng. y l ni dung ca phn phng php nghin cu trong cng nghin cu hay bo co khoa hc. Sau khi thu thp c s liu (i lng hay tnh cht ca cc i tng nghin cu), kt qu ca phn tch s liu (thng tin) c trnh by trong phn kt qu nghin cu. phn bn lun,tc gi s nh gi xem cc thng tin c tr li c cu hi nghin cu hay khng v cu tr li ca cu hi nghin cu chnh nhm gip gii quyt vn nghin cu l kin thc mi c to ra.Nh vy, mt bo co khoa hc s gm cc phn chnh: 1) t vn v mc tiu nghin cu 2) Tng quan ti liu 3) Phng php v i tng 4) Kt qu nghin cu 5) Bn lun v 6) Kt lun.Cc c im ca mt nghin cu khoa hc tt Mt nghin cu khoa hc tt c cc c im sau:1LastJM. Adictionaryof Epidemiology. NewYork: International epidemiologyassociation 1997; 1462VarkevisserC, PathmanathanI, BrownleeA.Designingandconductionghealthsystem research projects. IDRC, Ottawa 19911- Phi tp trung vo cc vn u tin trong chm sc y t- Phi c tnh nh hng vo hnh ng v ra cc gii php- Phi c tnh thi s: kt qu phi c kp thi a ra cc quyt nh ng n.- Thit k nghin cu n gin vthc hin trong thi gian ngn- Nn c tnh cht chi ph - hiu qu. Tt nht nu nghin cu c tin hnh vi chi ph thp v do cc nhn vin, cn b y t thc hin cng vi cng vic hng ngy.- Kt qu phi c trnh by theo hnh thc hu dng cho cc nh qun l, nh hoch nh chnh schv cng ng: Cn c tm tt nhng kt qu ch yu ca nghin cu v nu bt nhng im l th cho i tng ca bn bo co. Da theo kt qu c th trnh by gii php gii quyt mt vn v so snh u khuyt im ca vic tin hnh gii php v khng tin hnh gii php.- Nghin cu cn phi c nh gi khng ch da vo s cc bi bo c xut bn m cn phi xem xt s nh hng ca n n chnh sch y t hay thay i cung cch phc v v cui cng l tc ng ln sc kho ngi dn.i vi nghin cu y t cng cng cn phi t them hai c im sau:- S tt hn nu c s tham gia ca nhiu ngnh, nhiu khoa- Nghin cu cn c tnh cht tham gia ca mi thnh vin c lin quan trong tt c cc bc ca qu trnh tin hnh nghin cu2i cng v thng k v thng k m tMt s nh nghaThng k l phng php khoa hc dng thu thp, tm tt, trnh by v phn tch s liu.S liu: Kt qu c c do vic quan st hay thu thp mt bin s cc i tng khc nhau hay thi gian khc nhau.Th d:Khi ti quan st gii tnh ca cc hc vin trong lp, ti c s liu l:Nam, nam, n, n, n, nam, n, v.vTh d: Mt nh nghin cu o nng hemoglobin ca 70 thai ph c kt qu nh sau:10.2 13.7 10.4 14.9 11.5 12.0 11.013.3 12.9 12.1 9.4 13.2 10.8 11.710.6 10.5 13.7 11.8 14.1 10.3 13.612.1 12.9 11.4 12.7 10.6 11.4 11.99.3 13.5 14.6 11.2 11.7 10.9 10.412.0 12.9 11.1 8.8 10.2 11.6 12.513.4 12.1 10.9 11.3 14.7 10.8 13.311.9 11.4 12.5 13.0 11.6 13.1 9.711.2 15.1 10.7 12.9 13.4 12.3 11.014.6 11.1 13.5 10.9 13.1 11.8 12.2v nhng con s ny c gi l s liu.Cn lu s liu phi lin kt vi mt bin s nht nh. Nu ti quan st gii tnh ngi ny, tui ca ngi khc, qun o ca mt ngi khc na th kt qu quan st c khng phi l s liu.Bin s v cc loi bin sBin s l nhng i lng hay nhng c tnh c th thay i t ngi ny sang ngi khc hay t thi im ny sang thi im khc.Nh vy bin s c th th hin i lng hay c tnh. -Nu bin s th hin mt i lng n c gi l bin s nh lng (quantitative variable). Bin s nh lng c th cn c chia thnh bin s t s - ratio variable(c gi tr khng tuyt i) v bin s khong interval variable (khng c gi tr khng tuyt )- Nu bin s nhm th hin mt c tnh, bin s c gi l bin s nh tnh. Bin s nh tnh cn c chia lm 3 loi: - Bin s nh gi binary variable (khi ch c 2 gi tr) - Bin s danh nh nominal variable (khi c 3 hay nhiu hn cc gi tr v cc bn thn cc gi tr khng c tnh cht th t)- Bin s th t - ordinal variable (khi c 3 hay nhiu hn cc gi tr v cc bn thn cc gi tr c tnh cht th t - Ngoi ra c khi bin c khng ch c quan tm v phng din n c xy ra hay cha xy ra m cn c quan tm v phng din bin c xy ra vo lc no. Th d sau khiiu tr bnh nhn ung th chng ta khng ch quan tm bnh nhn c t vong hay khng m cn quan tm bnh nhn bnh nhn t vong bao nhiu lu sau khi iu tr v nu bnh nhn cha t vong, bnh nhn sng c bao lu. Phng php m t tm tt v trnh by s liu3-T l cho tng gi tr nul bin th t hay danhnh- T l cho gi tr tiu biunu l bin nh gi-T l cho tng gi tr nul bin th t hay danhnh- T l cho gi tr tiu biunu l bin nh giCc s thng k m tC hai loi thng k m t: thng k m t khuynh hng tp trung v thng k m t tnh phn tn.Thng k m t khuynh hng tp trungThng k m t khuynh hng tp trung c th l trung bnh (mean), trung v (median) v yu v (mode). Nhng thng k ny cho bit gi tr tiu biu cho s liu.Th d: c hai loi thuc h p A v B. Gi s c 5 i tng sau khi s dng thuc h p A s c huyt p 110 - 115 -120 - 125 -130 v 5 i tng khc sau khi s dng thuc h p B s c huyt p 120 - 125 - 130 - 135 - 140. Con s tiu biu nht cho bit tc dng cathuc A l huyt p trung bnh sau khi s dng thuc A v l 120. Con s huyt p trung bnh ny thp hn huyt p trung bnh sau khi s dng thuc B cho bit thuc A c tc dng mnh hn.Trung bnh ca s liu, c k hiu l (x (c l x gch) l tng cc gi tr ca s liu chia cho s ln quan st (N).NxxiTh d: S liu v huyt p tm thu ca 5 i tng l 120, 125, 130, 135, 150. Huyt p tm thu trung bnh s l 1321325150 125 130 125 120+ + + +NxxiDo khng th thc hin cc php ton s hc trn cc bin s nh tnh (danh nh v th t) chng ta ch c th tnh trung bnh cho s liu ca bin s nh lng.Nu chng ta sp xp s liu theo th t, gi tr ng gia c gi l trung v. Nu c hai gi tr cng ng gia, trung bnh cng ca hai gi tr ny l trung v.4Th d: S liu v huyt p tm thu (mmHg) ca 5 i tng l 120, 125, 130, 135, 150. Trung v ca huyt p tm thu l gi tr ng gia v bng 130S liu v chiu cao (cm) ca 6 ngi l 153, 155, 160, 162, 165, 161. tnh trung v, trc tin chng ta phi sp xp s liu ny: 153, 155, 160, 161, 162, 165. Do c hai gi tr 160 v 161 cng gia, trung v s l (160+161)/2 = 160,5 cmDo bn cht ca bin s danh nh khng th sp c theo th t, chng ta ch c th tnh trung v ca s liu nh lng v s liu ca bin s th t.Ngoi ra yu v (mode) cng c s dng lm con s thng k tiu biu. Yu v l gi tr xut hin ph bin nht (c tn sut cao nht).Th d: S liu v huyt p tm thu (mmHg) ca 5 i tng l 120, 125, 130, 135, 150. Trong trng hp ny khng c yu v.im s ca 5 hc sinh l 5, 5, 6, 7, 9. Yu v ca im s l 5.Trong mt p c 361 gia nh ngi Kinh, 120 gia nh ngi Khmer v 27 gia nh ngi Hoa. Yu v ca bin s dn tc l dn tc Kinh.Trong mt s liu c th, c th khng c yu v, c th c mt yu v hoc hai hay nhiu yu v. y l khuyt im chnh ca s thng k ny. Do vy ngi ta thng ch dng yu v cho bin s danh nh hay trong cc trng hp c bitC th s dng trung bnh, trung v hay yu v cho bin s nh lng. Khi bin s nh lng c phn phi bnh thng (hnh chung) th ba con s ny xp x bng nhau v khi ngi ta thng tnh trung bnh bi v trung bnh c nhng c tnh ton hc mnh. Tuy nhin nu s liu b lch th con s trung v phn nh gi tr tiu biu mt cch chnh xc hn.Th d: Bnhnhnb lot ddy- ttrngciutr theomt phcdit vi khun Helicobacter. Sau iu tr, bnh nhn c theo di v ghi nhn thi gian k t khi s dng thuc n lc bt u ci thin triu chng au. 10 bnh nhn thi gian ny (ngy ) l nh sau: 1, 2, 2, 2, 2, 2, 3, 3, 3, 30. Bnh nhn c thi gian t lc iu tr n lc gim triu chng l 30 ngy trn thc cht l bnh nhn khng p ng vi iu tr. Trung v v trung bnh ca s liu l 2 v 5 ngy. Con s trung v phn nh chn thc hn bi v vi t cch l mt bc s lm sng t s liu trn c th nhn xt rng mt bnh nhn tiu biu s gim au sau 2 ngy dng thuc. Con ss 30 trong th d trn c gi l s ngoi lai (outlier) v lm s liu b lch. Nhn chung, khi s liu b lch th con s trung bnh s b nh hng rt nhiu v khng phn nh gi tr tiu biu nh con s trung v.Thng k m t tnh phn tn:C 3 thng k m t tnh phn tn: lch chun, khong t phn v v phm vi ca s liu.Vic la chn thng k m t tnh phn tn c trnh by trong bng 2.Thng k m t tnh phn tn c tm quan trng th hai sau con s m t khuynh hng tp trung. Th d: Thuc h p A c s dng trn 5 bnh nhn v huyt p tm thusau khi dng thuc l 110, 115, 120, 125 v 130. Thuc h p B c s dng trn 5 bnh nhn v c huyt p sau s dng thuc l 100, 110, 120, 130, 140.Nh vy hai thuc h p ny c hiu qu h p l tng ng (bi v trung bnh ca hai s liu l bng nhau) nhng kt qu ca thuc B phn tn hn v iu ny lm thuc B tr nn km an ton. lch chun (standard deviation - vit tt l SD hay s) l con s nh gi mc phn tn v c tnh theo cng thc:Nh vy lch chun phn nh khong cch trung bnh ca s liu so vi gi tr tiu biu. Khi nim lch chun ch c th p dng cho bin s nh lng bi v chng ta c th thc hin cc php ton s hc trn cc i lng nhng khng th thc hin trn cc gi tr ca bin s nh tnh l cc c tnh.Th d: S liu v huyt p tm thu (mmHg) ca 5 i tng l 120, 125, 130, 135, 150. Trung bnh ca huyt p l 132 v lch chun bngniiNx xs121) (55 , 11 5 , 13245304324 9 4 49 1441 5) 132 150 ( ) 132 135 ( ) 130 132 ( ) 132 125 ( ) 132 120 (1) (2 2 2 2 212 + + + + + + + + niiNx xsPhng sai v mt t nguyn l bnh phng ca lch chun. Phng sai (variance) c th c k hiu v Var hay s2 v c tnh theo cng thc sau:niiNx xs1221) (Phm vi ca s liu l tt c cc gi tr ca s liu t gi tr nh nht n gi tr ln nht.Th d: S liu v huyt p tm thu (mmHg) ca 5 i tng l 120, 125, 130, 135, 150. Phm vi ca bin s huyt p l 120 n 150.Th d: Thuc h p A c s dng trn 5 bnh nhn v huyt p tm thusau khi dng thuc l 110, 115, 120, 125 v 130. Thuc h p B c s dng trn 5 bnh nhn v c huyt p sau s dng thuc l 100, 110, 120, 130, 140. S liu ca thuc B ctnh phn tn cao hn do phm vi thay i t 100-140 trong khi phm v ca s liu thuc A ch t 110-130.Khong t phn v (inter-quartile): Nu chng ta chia s liu sp theo th t lm 2 phn u nhau, khong t phn v l khong cch ca trung v phn trn v trung v phn di.Th d: S liu v huyt p tm thu (mmHg) ca 5 i tng l 120, 125, 130, 135, 150. S liu ny c chia lm 2 phn: phn 1 gm 120, 125, 130 v phn 2 gm 130, 135, v 150. Trung v ca phn trn l 125 - trung v ca phn di l 135, do phm t phn v l 125-135.Do bn cht ca khong t phn v l trung v ca phn s liu trn v phn s liu di, cng ging nh trung v, khong t phn v khng b nh hng bi cc gi tr ngoi lai nh trong trng hp ca lch chun. Cng nh trung v, khong t phn v ch c th p dng cho bin s nh lng hay th t.Cu hi: Phn tch trn my tnh v bin s hemoglobin cho kt qu sau. Hy th c v l gii kt qu:Variable | ObsMean Std. Dev. MinMax-----------+-----------------------------------------------------hemoglobin |7011.98429 1.4161228.8 15.1Phng php trnh by s liuS liu c th c trnh by thnh bng hoc cc th.Trnh by bng:Phn phi tn sut ca bin s nh tnhS liu ca bin s ri rc c th c trnh by di dng mt phn phi tn sut. Phn phi tn sut l mt bng ch ra tn sut xut hin ca tng gi tr ri rc ca bin s (Bng 1). Nh vy bng phn phi tn sut gm 2 ct, mt ct lit k cc gi tr ca bin s v mt ct trnh by tn sut tng ng ca cc gi tr .Table 1. Phn phi gii tnh ca 69 hc sinh lp cm thng trng mm non 23 thng 11, Huyn Hc mnGii S tr Phn trm6Nam 45 65%N 24 35%Tng s 69 100%Bng trn l bn phn phi tn sut ca gii tnh. Bi v gii tnh c 2 gi tr nam v n nn ta lit k 2 gi tr ny mt ct. ct th nh ta ghi tn sut tng ng ca cc gi tr ny. i khi bng phn phi tn sut c thm ct phn trm nh trong th d trn. Bng 2 l mt th d khc v bng phn phi tn sut.Table 2. Phng php ca 600 tr trong bnh vinPhng php S sinh Phn trmSinh thng 478 79,7Sinh forceps 65 10,8Sinh m 57 9,5Tng s 600 100,0Phn phi tn sut ca bin s nh lngNu bin s l bin s lin tc chng ta khng th lit k tt c cc gi tr ca bin s. Trong trng hp ny chng ta c th nhm (lm trn) gi tr ca bin s li.C th cc bc xy dng bng phn phi tn sut cho bin s nh lng nh sau:1- Tm phm vi (gi tr cc tiu v gi tr cc i) ca s liu. Trong th d v hemoglobin ca 70 ph n phm vi l 8,8 n 15,12. Chia phm vi s liu ra lm n khong vi rng ca mi khong l d. Cn lu rng mi khong d nn l i lng chn nh 1, 2, 5, 10 hay 0,5, 0,2 v s cc khong n nn t 5-12 (trung bnh l 7-8). Trong th d trn ta c th chia phm vi ra lm 8khong vi chiu rng khong bng 1 n v. Khi cc khong l: 8-8,9; 9-9,9; 10-10,9; 11-11,9; 12-12,9; 13-13,9; 14-14,9; 15-15,9.3. m cc gi tr thch hp vo khong nh trcHemoglobin(g/100ml)m8-8,9 19-9,9 11110-10,9 11111111111111-11,9 111111111111111112-12,9 11111111111113-13,9 1111111111114-14,9 111115-15,9 14. Xy dng bng phn phi tn sut vi bin s v cc khong gi tr ca bin s v tn sut 7tng ng vi cc khong gi tr . Chng ta cng c th thm vo ct phn trm v ct phn trm tch ly(nu thch hp)Table 3. Hemoglobin ca 70 ph nHemoglobin Tn sut Phn trm Phn trm tch ly8-8,9 1 1.43 1.439-9,9 3 4.29 5.7110-10,9 14 20.00 25.7111-11,9 19 27.14 52.8612-12,9 14 20.00 72.8613-13,9 13 18.57 91.4314-14,9 5 7.14 98.5715-15,9 1 1.43 100.00Th d nh nu bin s l chu vi vng cnh tay ca tr chng ta c th lm trn chu vi vng cnh tay n 1 cm. Khi ta c th xem thang o ca bin s l ri rc v trnh by bng phn phi tn sut ca bin s (bng 2).Table 4. Phn phi s o vng cnh tay ca 69 tr lp cm thng nh tr 23 thng 11, Hc mn.Vng cnh tay Tn sut Phn trm Phn trm tch ly13- |t| = 0.0012P > t = 0.9994Tr li:Tr trai c trng lng s sinh trung bnh l 3211.28 gram, ca tr gi l 3044.13 gram.Vi gi tr t = 3,2654 v mc ngha (p-value) l 0.0012 chng ta kt lun c s khc bit v trng lng s sinh gia tr trai v tr gi (p=0.0012). 6. Hy so snh trng lng s sinh ca con b m tng huyt p v b m khng tng huyt p.Hng dn: Theo gii thut c trnh by u chng, so snh trng lng (bin ph thuc c phn phi bnh thng) 2 nhm trc tin chng ta cn phi xem phng sai ca 2 nhm m tng huyt p v m khng tng huyt p c bng nhau hay khng. Nu phng sai 2 nhm tng ng chng ta c th s dng t-test thng thng (t-test phng sai ng nht). Nu phng sai 2 nhm khng tng ng, chng ta phi s dng t-test phng sai khng ng nht hay kim nh phi tham s.150Kim nh 1: So snh2 phng sai so snh trung bnh ca mt bin nh lng hai hay nhiu nhm, chng ta s dng menu Statistics :: Summaries, tables, &tests :: Classical tests of hypothesis :: Group variance comparison test.Sau khi ca s sdtest - Group variance comparison test chng ta a bin tlsosinh vo hp vn bn Variable name v bin tang_ha vo hp vn bn Group name variable ri nhp vo nt lnh OK.Kt qu c trnh by nh sau:. sdtest tlsosinh, by( tang_ha )Variance ratio test------------------------------------------------------------------------------ Group | ObsMeanStd. Err. Std. Dev. [95% Conf. Interval]---------+-------------------------------------------------------------------- Ha bt | 5523191.53125.58435601.09623141.2763241.786 Ha tang |892742.15786.17222812.94712570.9082913.406---------+--------------------------------------------------------------------combined | 6413129.13725.78336652.78273078.5073179.767------------------------------------------------------------------------------Ho: sd(huyet ap) = sd(huyet ap) F(551,88) observed = F_obs =0.547F(551,88) lower tail = F_L = F_obs =0.547F(551,88) upper tail = F_U = 1/F_obs =1.829 Ha: sd(1) < sd(2) Ha: sd(1) != sd(2)Ha: sd(1) > sd(2)P < F_obs = 0.0000 P < F_L + P > F_U = 0.0003 P > F_obs = 1.0000Kt qu cho thy gi tr p = 0,0003 c ngha l phng sai ca trng lng lc sinh ca 2 nhm khng ng nht. V vy chng ta khng th dng t-test phng sai ng nht m phi s dng t-test phng sai khng ng nht (kim nh 2A) hay kim nh phi tham s (kim nh 2B).Kim nh 2A: so snh 2 trung bnh t-test phng sai khng ng nht so snh trung bnh ca mt bin nh lng hai hay nhiu nhm, chng ta s dng menu Statistics :: Summaries, tables, & tests :: Classical tests of hypothesis :: Group mean comparison test (xem li cu 4) v bin tlsosinh vo hp vn bn Variable name; bin tang_ha vo hp vn bn Group name variable ca ca s ttest- group mean comparison. Cn lu nh du vo hp kim Unequal variances ri nhp vo nt OK.151Kt qu trnh by nh sau:. ttest tlsosinh, by(tang_ha) unequalTwo-sample t test with unequal variances------------------------------------------------------------------------------ Group | ObsMeanStd. Err. Std. Dev. [95% Conf. Interval]---------+-------------------------------------------------------------------- ha bt | 5523191.53125.58435601.09623141.2763241.786 ha tang |892742.15786.17222812.94712570.9082913.406---------+--------------------------------------------------------------------combined | 6413129.13725.78336652.78273078.5073179.767---------+--------------------------------------------------------------------diff |449.373589.88999271.1197627.6273------------------------------------------------------------------------------Satterthwaite's degrees of freedom:104.069 Ho: mean(ha bt) - mean(ha tang) = diff = 0 Ha: diff < 0 Ha: diff != 0Ha: diff > 0 t = 4.9991t = 4.9991t = 4.9991 P < t = 1.0000P > |t| = 0.0000P > t = 0.0000Tr li:Con b m b tng huyt p c trng lng s sinh trung bnh l 2742 gram, con ca b m khng tng huyt p l 3192 gram. S khc bit ny c ngha thng k vi p |z| = 0.00007. Hy so snh trng lng s sinh ca tr sinh ra t con ca cc nhm ngh nghip khc nhau ca ngi m.Hng dn: so snh trung bnh ca mt bin nh lng nhiu nhm, chng ta phi s dng phng php phn tch ANOVA mt chiu.S dng menu Statistics :: ANOVA/MANOVA :: oneway analysis of varianceDo chng ta mun phn tch tc ng ca yu t ngh nghip m (nghenghiep) ln trng lng sinh ca tr (tlsosinh) khi ca s oneway hin ln, ta tin hnh cc bc sau:Bc 1: t con tr vo hp vn bn Response variableBc 2: a con tr vo ca s Variables v nhp vo bin tlsosinh a bin ny vo hp vn bn Response Variable.Bc 3: t con tr vo hp vn bn FactorBc 4: a con tr vo ca s Variables v nhp vo bin nghenghiep a bin ny vo hp vn bn Factor.Bc 5: nh du vo hp kim Produce summary table th hin thng k m t trng lng s sinh trung bnh cc nhm ngh nghip154Bc 6: nh du vo hp kim Scheffe c kim nh so snh trng lng trung bnh tng cp i ngh nghip khc nhauBc 7: Nhp vo nt lnh OK Trn ca s Output, trn cng thng k m t ca s liuv trng lng s sinh theo nhm tui ca m:nghe nghiep |me - 1=tu | do, 2=cong | Summary of trong luong so sinhnhan, | (gram)3=vien chuc |Mean Std. Dev. Freq.------------+------------------------------------tu do | 2981.4135 643.76283 104cong nhan |3118.084 646.69338 238vien chuc | 3189.3177 654.19649 299------------+------------------------------------Total | 3129.1373 652.78265 641Conbmnghnghipt doctrng lng trung bnh l 2981 gram, ca b m vi ngh nghip l 3118 gram, ca b m vi ngh nghip vin chc l l 3190 gram. Chng ta bit kim nh ANOVA c th s dng kim nh s khc bit v trung bnh ca nhiu nhm, nhng trc tin chng ta hy kim tra cc iu kin ca phn tch ANOVA l (a) bin s ph thuc c phn phi bnh thng - iu ny c xc nhn t th ca trng lng s sinh v (b) phng sai ca bin ph thuc cc nhm bng nhau - iu ny cng c xc nhn qua thng k Bartlett vi p-value l 0,973. Analysis of VarianceSourceSS dfMSF Prob > F------------------------------------------------------------------------Between groups3381483.562 1690741.784.00 0.0187 Within groups 269338638638 422160.875------------------------------------------------------------------------Total272720122640426125.19Bartlett's test for equal variances:chi2(2) = 0.0558Prob>chi2 = 0.973V vy trong trng hp ny kim nh ANOVA l c gi tr. Ta c kt qu ca bng ANOVA. 155Chng tac c gi tr F = 0.0187 v mc ngha (p-value) l 0.9723 chng ta kt lun khng c s khc bit v trng lng s sinh con ca nhng b m c ngh nghip khc nhau. Vi kt lun ny chng ta c th kt lun l c t nht c 1 cp i (2 nhm) ngh nghip ca m c s khc bit v trng lng con nhng chng ta khng bit l s khc bit ny cp i ngh nghip no. bit cp i no c s khc bit ta xem kt xut ca so snh sau kim nh (post-hoc test) ca Scheffe: Comparison of trong luong so sinh (gram)by nghe nghiep me - 1=tu do, 2=cong nhan, 3=vien chuc(Scheffe)Row Mean-|Col Mean |tu do cong nha---------+----------------------cong nha |136.671 |0.202 |vien chu |207.90471.2337 |0.0200.451Kt qu ca kim nh Scheffe c trnh by theo bng v mi ca bng c 2 con s: con s trn th hin s khc bit v trng lng ca ngh nghip ca hng so vi ngh nghip ca ct v gi tr di th hin gi tri p (mc ngha) ca s khc bit ny. Da vo gi tr p, c th kt lun c s khc bit v trng lng s sinh ca con 2 nhm ngh nghip vin chc v t do (gi tr p=0,020) v nhm ngh nghip vin chc c trng lng trung bnh cao hn nhm ngh nghip t do l 207,9 gram.Nhc li l thuyt v Tng quan v c lngTng quan l s o mc hai bin s nh lng cng thay i vi nhau. C nhiu loi h s tng quan, nhng chng u c gi tr t -1 n 1. Nu chng c gi tr dng c ngha l hai bin s ng bin vi nhau, nu chng c gi tr m ngha l hai bin s nghch bin. Gi tr tuyt i ca h s tng quan cng gn mt ngha l hai bin s c lin h cht vi nhau v vai tr ca sai s ngu nhin s t hn. Nu h s tng quan c gi tr bng zero c ngha l hai bin s c lp v khng quan h g vi nhau. Khi tr tuyt i ca h s tng quan bng mt c ngha l hon ton khng c sai s ngu nhin. Bnh phng ca h s tng quan (r2) th hin t l cc bin thin ca bin s ph thuc c th c gii thch bng bin s c lp.Loi h s tng quan c s dng ph bin nht l h s tng quan Pearson r: 2 2) ( ) () )( (y y x xy y x xri ii iL gii ngha ca h s tng quan: - H s tng quan lun lun nm trong on [-1,1]- H s tng quan r dng chng t hai bin s l ng bin; h s tng quan r m chng t hai bin s l nghch bin; h s tng quan bng zero nu hai bin khng lin h. - Tr s tuyt i ca h s tng quan r ni ln mc lin quan gia hai bin s. Nu tr tuyt i ca r bng 1 (r=1 hay r=-1), quan h hon ton tuyn tnh ngha l tt c cc im nm trn ng hi quy (Hnh 9.2 d v 9.2f). Nu tr tuyt i ca r nh hn 1 s c cc im s liu phn tn chung quanh ng hi quy.- Bnh phng ca h s tng quan (r2) th hin t l bin thin ca bin s ph thuc c gii thch bng s bin thin ca bin s c lp (nu mi lin h ny l nhn qu)- Nu r=0, khng c mi lin h tuyn tnh gia hai bin s. iu ny c ngha l (1) khng c mi lin h g gia hai bin s hoc(2) mi lin h gia hai bin s khng phi l tuyn tnh.156- Theo quy c, quan h vir t 0,1 n 0,3 l quan h yu, t 0,3 n 0,5 quan h trung bnh v trn 0,5 l quan h mnh. iu quan trng l s tng quan gia hai bin s cho thy s lin h nhng khng nht thit c ngha l c quan h 'nhn qu'. kim nh h s tng quan Pearson c thc s khc 0 hay khng, kim nh t c th c s dngt rnr212 c phn phi student vi n-2 t do.Hi quyHi quy l mt m hnh ton hc m t s bin i ca mt bin s ny theo nhng bin s khc.Mt phng trnh hi quy c th c dng nh sau:cn nng (kg) = 6,85 + 0,18 x thng tui(phng trnh hi quy tnh cn nng ca tr t 9 n 40 thng tui theo thng tui)theo phng trnh ny ngi ta gi:cn nng: bin s ph thucthng tui: bin s c lp6,85: h s ca hng s (Constant), hay cn gi l im chn (intercept)0,18: h s (Coeficient)ca bin s thng tui hay cn gi l dc (Slope) ca ng hi quy9. Vphntn(scattergram) giacabinstui thai (tuoithai) vtrnglngthai (tlsosinh).Hng dn: s dng menu Graphics :: Overlaid twoway graph hin ra ca s twoway Twoway graphs157Trn ca s twoway Twoway graphs, nhp tn bin s ph thuc vo hp Y-axis variable v tn bin s c lp vo hp X-axis variable sau nhp OK xem biu phn tn. Cch lm c th tng bc nh sau:Bc 1: Trn hp combo Type chn ScatterBc 2: t tn bin s c lp (tuoithai) vo vn bn XBc 3: t tn bin s ph thuc (tlsosinh) vo vn bn YBc 4: Nhp nt lnh OKC th cho th phn tn. Tuy nhin chng ta c th thm cc ty chn thc hin cc yu cu sau: B sung tiu trng lng tr s sinh (gam)" cho trc tung Cho cc gi tr trc y t 500 n 5000 gram v chia cc khong 500 gram. B sung tiu tuoi thai (tuan tuoi)" cho trc honh Cho cc gi tr ca trc x t 24 tun tui n 42 tun tui v chia lm cc khong 4 tun Bng cch trong ca s Trn ca s twoway Twoway graphs thc hin cc bc:Trn th Plot 1:Bc 1: Trn hp combo Type chn ScatterBc 2: t tn bin s c lp (tuoithai) vo vn bn X158Bc 3: t tn bin s ph thuc (tlsosinh) vo vn bn YTrn th Y-Axis:Bc 4: Trn hp vn bn Title g "Trong luong tre so sinh (gam)"Bc 5: Trn hp vn bn Rule g quy tc "500(500)5000"Bc 6: Trn hp combo Angle chn "Horizontal" Trn th X-Axis:Bc 7: Trn hp vn bn Title g "Tuoi thai (tuan)"Bc 8: Trn hp vn bn Rule g quy tc "24(2)42"V nhp vo nt lnh OK.Tr li: C s tng quan thun tuyn tnh gia trng lng s sinh v tui thai. Mi tng quan ny kh cht do m my c tnh cht i ln (khi n i v phi) v c ng knh bnh hn nhiu so vi ng knh ln.10. Hy xc nh h s tng quan gia trng lng s sinh (tlsosinh), tui thai (tuoithai) v tui ca m (tuoime)Hngdn: SdngmenuStatistics :: Summaries, tables, &tests:: Summarystatistics :: Pairwise correlations.159Khi hp thoi pwcorr Pairwise correlations of variables s hin ra. Tin hnh cc bc sau:Bc 1: Nhp con tr chut vo hp vn bn VariablesBc 2: a con tr chut vo ca s Variables v nhp vo cc bin tlsosinh, bin tuoithai v bin tuoime tn 3 bin ny xut hin hp vn bn Variables.160Bc 3: nh du vo hp kim Print significance level for each entryBc 4: nh du vo hp kim Significance level for displaying with a star.Bc 5: Nhp vo nt lnh OK xem kt qu.. pwcorr tlsosinh tuoithai tuoime, sig star(5) |tlsosinhtuoithai tuoime-------------+---------------------------tlsosinh | 1.0000 | |tuoithai | 0.7376*1.0000 | 0.0000 |tuoime | 0.0337 0.0151 1.0000 | 0.3941 0.7026Tr li: Chng trnh cho kt qu h s tng quan ca trng lng thai vi trng lng thai l 1, gia trng lng thai v tui thail 0.7376 (gi tr p=0,0000), gia trng lng thai v tui ca m l 0,0337 (gi tr p = 0,3941). Nh vy c s tng quan mnh c ngha thng k gia trng lng thai v tui thai trong khi s tng quan gia trng lng thai v tui m rt yu v khng c ngha thng k. Do c s lin h c ngha thng k (gi tr p F=0.0000Residual | 124365805 639194625.673 R-squared =0.5440---------+------------------------------ Adj R-squared =0.5433 Total | 272720122 640 426125.19 Root MSE=441.16tlsosinh |Coef. Std. Err. t P>|t| [95% Conf. Interval]---------+--------------------------------------------------------------------tuoithai | 206.6412 7.484572 27.609 0.000 191.9439221.3386 _cons |-4865.245 290.0814-16.772 0.000-5434.873 -4295.617Tr li: H s tng quan bnh phng R-squared = 0.544= 54.4% ni ln tui thai c th gii thch cho 54.4% s thay i v trng lng s sinh. Bng ANOVA cho bitc tng cc sai lch ca bnh phng trng lng s sinh 272.720.122 (272.7 triu) m phng trnh hi quy c th gii thch cho 148.3 triu ca s sai lch ny (nh vy cn 124.4 triu tng bnh phng sai lch cha c gii thchgi l Residual Sum of Square v gi tr 0.45 chnh l gi tr 148.3/272.7). Mc ngha c trnh by trong bng ANOVA cho bit mc ngha ca phng trnh. Da vo bng cc h s chng ta c th xy dng phng trnh hi quy nh sau:Trng lng s sinh = -4865.245 + 206.641 x tui thai (tnh theo tun).Mc ngha (P-value) ca bin s tui thai (Gestational age) l kt qu ca kim nh ngha ca bin s ny trong phng trnhc thc s khc khng hay khng.H s (coefficient) ca bin s c lp ni ln s thay i ca bin s ph thuc khi bin s c lp thay i mt n v. Trong phng trnh ny (vi bin s c lp l TUOITHAI v bin s ph thuc l TLSOSINH) chng ta c th l gii nu a tr ln hn 1 tun tui trng lng lc sanh ca n s tng thm 206.641 gram.12. Hy xy dng phng trnh hi quy ca trng lng thai theo tui thai, gii tnh ca tr v huyt p cao ca m.Hng dn: S dng phng php hi quy n bng cch nhp vo menu"Statistics :: Linear regression and related ::Linear regression" hin ra hp thoi regress Linear regressionNhp tn bin s ph thuc (tlsosinh) vo hp Dpendent variable v tn cc bin s c lp (tuoithai gioi tang_ha) vo hp Idependent variables, ri nhn OK tip tc. Khi hp thoi 162chn on s hin ra. Tuy nhin nu chng ta khng quan tm n vic chn on cc vn trong phng trnh hi quy chng ta hy nhp vo nt Cancel.. regress tlsosinh tuoithai gioi tang_haSource | SS df MSNumber of obs = 641-------------+------------------------------ F(3, 637) =275.43 Model | 153998584 351332861.4 Prob > F=0.0000Residual | 118721538 637 186376.04 R-squared =0.5647-------------+------------------------------ Adj R-squared =0.5626 Total | 272720122 640 426125.19 Root MSE=431.71------------------------------------------------------------------------------tlsosinh |Coef. Std. Err.tP>|t| [95% Conf. Interval]-------------+----------------------------------------------------------------tuoithai | 201.4248 7.54144126.71 0.000 186.6157216.2339gioi | 167.8167 34.17884 4.91 0.000 100.6999234.9335 tang_ha |-142.1450.8685-2.79 0.005-242.0302 -42.24979 _cons |-4729.048 294.1447 -16.08 0.000-5306.659 -4151.438------------------------------------------------------------------------------Tr li: Chng ta tm c r2(R-squared) l 0.5647 cho thy phng trnh hi quy gii thch c 56.47% s bin thin ca trng lng thai v iu ny cho thy m hnh c c gii tnh v tng huyt p gii thch tt hn so vi m hnh ch c tui thai (r2=0.54). Chng ta cng c th vit c phng trnh hi quy theo kt qu trn:Trng lng thai = -4729.048 + tui thai x 201.425 - tng huyt p x 142.14 + gii x167.81710. Bn c gi g trnh by phng trnh hi quy mt cch d hiu hn i vi ngi khng chuyn v thng k.Hng dn: Bi v ngi khng chuyn v thng k hay ngi cha c lm quen vi phng php m ho s khng bit lm sao nhn tng huyt p vi 142.14 hay gii vi 167,817. Chng ta nh li quy c ca tp tin ny:Bin tng huyt p (tang_ha) c gi tr =0 nu m khng b tng huyt pBin gii tnh (gioi) c gi tr =0 nu tr l tr gia) Do phng trnh hi quy i vi tr gi c m khng tng huyt p l:Trng lng thai = -4729.048 + tui thai x 201.425(a)b) tr trai vi m khng tng huyt p, trng bin s ph thuc ca phng trnh hi quy s tng ln 167,817 gram nn phng trnh hi quy s lTrng lng thai = -4561.23 + tui thai x 201.425(b)c) tr gi vi m b tng huyt p, trng bin s ph thuc ca phng trnh hi quy s s gim i 142,14 gram so vi phng trnh (a) nn phng trnh hi quy cho nhm ny lTrng lng thai = -4871.19 + tui thai x 201.425 d) tr trai vi m b tng huyt p, trng bin s ph thuc ca phng trnh hi quy s s gim i 142,14 gram so vi phng trnh (b) nn phng trnh hi quy cho nhm ny lTrng lng thai = -4703.37+ tui thai x 201.425 Do cc mc ngha (p-value) ca bin s u nh hn 0.05 nn tt c cc bin s c lp ca m hnh u c ngha thng k v khng nn loi b khi m hnh.13. Xt hai m hnhtrng lng thai = tui thai + tng huyt p m + gii tnh (cho h s ca bin s tui t hai l 201.4) trong khi m hnhtrng lng thai = tui thai (choh s ca bin s tui thai l 206.6). H s trong m hnh no l ph hp hn nh gi s tng trng ca trng lng thai.Tr li:Chng ta c th gi nh yu t tng huyt p ca m l yu t gy nhiu. Do tng huyt p ca m c th lm gim trng lng ca con v trong tng huyt p ca m ph bin hn nhm 163sanh thiu thng nn a tr sinh sm 1 tun b mt trng lng l 206.6 gram nhng iu ny l c do tc ng ca sanh non v c tc ng do tng huyt p mt s b m. Tuy nhin nhm khng b tng huyt p tr sanh non mt tun ch b mt c 201.4 gram v do con s 201.4 l ph hp hn nh gi s tng trng ca trng lng thai.Trn thc tin do con s 201.4 rt gn vi con s 206.6 nn c th b qua tc ng gy nhiu ca tng huyt p ca m ln tc pht trin thai.14. S dng kim nh t chng ta pht hin trng lng tr con cc b m b tng huyt p thp hn con nhng ngi khng tng huyt p l449.37 gram. Trong khi m hnh ca trng lng sinh theo tui thai, tng huyt p m v gii tnh cho h s ca bin tng huyt p l 142.14 gram. Hy l gii nhng s liu ny?Tr li: C hai con s 449.37 v 142.14 u ni ln s khc bit do tnh trng tng huyt p ca m nhng con s 449.37 l con s khc bit th v con s 142.14 l con s khc bit c hiu chnh theo thng tui v gii tnh. Da vo nhn xt trn ta c gii thch nhng con s ny nh sau: con cc b m b tng huyt p c trng lng nh con nhng ngi khng tng huyt p l 449.37 gram v iu ny do tc ng ca c tng huyt p, tui thai (v c tc ng ca gii tnh nhng gi s chng ta bit rng tc ng gy nhiu cao gii tnh l khng ng k). con cc b m b tng huyt p c trng lng nh con nhng ngi khng tng huyt p l 142.14 gram v iu ny do tc ng ca c tng huyt p khi khng xt n tc ng ca tui thai. Nh vy tc ng do sinh thiu thng l 449.37-142.14 = 307.23 gC a o h u y e ta p m e T r o n gl n g c o nS i n h t h i e ut h a n gC c h e k h a c1 4 2 . 1 4 g4 4 9 . 3 7 gNh vy % tc ng do c ch sinh thiu thng trong tng s tc ng ca tng huyt p m ln trng lng ca con l:% 68 68 . 037 . 44922 . 30737 . 44914 . 142 37 . 449 tho ong tacchnh hieu ong tac - tho ong tac Chng ta c th xem xt tc ng ca c ch sinh thiu thng trong khi so snh trng lng s sinh ca 2 nhm m tng huyt p v m khng tng huyt p bng cch so snh tui thai trung bnh gia 2 nhm. Nhm c m b tng huyt p c tui thai trung bnh l 37.3 tun trong khi nhm m khng b tng huyt p c tui thai trung bnh l 38.9 v s khc bit v tui thai l 1.6 tun. S khc bit v tui thai s gii thch cho khong 200 gram/tun x 1.6 =320 gram trng lng s sinh.164