chuong 3_thu thap xu ly so lieu nghien cuu

Chng 3. THU THP, X L S LIU NGHIN CU3.1. Mu va ly mu/chn mu 3.1.1. Cc khi ni m Thng khng th nghin cu ht ton b cc c th trong qun th, m ch thc hin trn mt b phn hay mt s c th i din gi l mu (sample). Ly mu hay chn mu (sampling): la chn mt b phn hay cc c th t mt qun th c lng cc c tnh ca ton th qun th. Tnh i din l yu cu quan trng nht ca mu va ly mu. Cc v d ly mu trong nghin cu KH Mi trng: Chn cc a im iu tra ti nguyn thin nhin Chn nhm ngi dn, hc sinh, iu tra v nhn thc mi trng Chn mu nc, khng khi, trong quan trc mi trng

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Chng 3. THU THP, X L S LIU NGHIN CU Phn loi cc phng php ly mu: Ly mu xc sut (probability sampling): cc c th ca mu c chn sao cho mi c th c c hi c chn nh nhau Gm cc phng php: Ly mu ngu nhin n gin (Simple Random Sampling) Ly mu h thng (Systematic Sampling) Ly mu phn tng (Stratified Sampling)

Ly mu phi xc sut (non-probability sampling): cc c th ca mu c chn khng ngu nhin hay khng c c hi c chn nh nhau.

Ly mu theo ch tiu (Quota sampling) Ly mu theo s thun tin (Convenience sampling)3-2

Chng 3. THU THP, X L S LIU NGHIN CU 3.1.2. L y m u ng u nhin n gi n Cch tin hnh: Chun b khung mu (sampling frame) Xc nh c mu (n n v) Chn n v mu bng: Rt thm Dng bng s ngu nhin Dng dy s, ngu nhin t my tnh

V d cch rt thm ngu nhin chn 100 sinh vin trong s, 1000 sinh vin nhm kho st v nhn thc mi trng, vit tn 1000 SV trn 1000 mu giy (khung mu), cho vo thng, nht ra 100 mu giy xc sut chn mi SV = 10%3-3

Chng 3. THU THP, X L S LIU NGHIN CU

u im: n gin Nn tng xc sut C bn so snh vi cc phng php khc

Nhc im: Phi lm khung mu (nh s, ghi tn) Thi gian v kinh ph cao (khi n ln) c trng nhm c th b b st t dng3-4

Chng 3. THU THP, X L S LIU NGHIN CU3.1.3. L y m u h th ng Ly mu hng lot theo khong cch nht nh (khong cch mu) khung mu nh 1 hng cc n v mu, v mu nh l mt chui lin tip ca cc im s c khong cch bng nhau theo hng dc. V d: Mun nghin cu 1 thnh vin trong mi nhm c 10 c th, qun th c 10 nhm (tng c th ca qun th l 100): nh s c th t 1-100: nhm 1 t 1-10; nhm 2 t 11-20; nhm 3 t 21-30; nhm 10 t 91-100. Sp xp th t cc n v mu (th d theo th t gia tng) Chn ngu nhin im u tin c gi tr < 10 (th d chn ngu nhin s, 7) S c th tip theo s cng thm l 10. Nh vy cc thnh vin c chn s c s th t l 7, 17, 27, 37, 47, 97.3-5


u im: Khng cn bit chnh xc ng nht hn Hn ch: Khng thch hp khi kho st cc c trng c tnh chu k.Chn mu h thng3-6


3.1.4. L y m u phn t ng Qun th c chia tng trc, sau o, mu c ly ngu nhin trong tng tng. Tin hnh: Phn tng (L = s tng) Xc nh c mu (n) Xc nh c mu tng tng: Bng nhau gia cc tng ni = n/L Phn b theo t l: ni = (Ni) (n/N)

Ly mu ngu nhin tng tng3-7


u im: chnh xc tng C c thng tin cho tng tng Li ch/chi ph hn

Cc kiu phn tng qun th thng gp: theo a ly, (thnh ph, tnh, huyn); theo vng sinh thi; theo gii tnh; theo tui; theo mc giu ngho, trnh hc vn, 3-8

Chng 3. THU THP, X L S LIU NGHIN CU V d: khi nghin cu v mc giu ngho ca mt vng nghin cu c 4 huyn (4 phn lp), mi huyn c s h gia nh khc nhau; ngi nghin cu mun thc hin 200 cuc phng vn h gia nh trong vng nghin cu, nh vy c mu ca mi huyn s c tnh theo t l phn trm trong Bng 3.1 nh sau: Bng 3.1. V d v cch chn mu phn lp

T ng3-9

Chng 3. THU THP, X L S LIU NGHIN CU Trong v d trn, nu s h ca 4 huyn gn nh nhau, ngi nghin cu ch cn chn 50 cuc phng vn trong mi huyn v sau chn mu ngu nhin trong mi lp. Cng trong nghin cu trn, nu ngi nghin cu khng phn chia ra thnh cc lp (huyn), m ly phng vn ngu nhin h gia nh trong ton vng nghin cu s dn n s liu thu thp s khng i din cho vng nghin cu, v mu c th tp trung mt huyn no .

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Chng 3. THU THP, X L S LIU NGHIN CUPhn nhiu tng ngha thc tin: V d: Gi s cn iu tra h gia nh ca mt tnh c 12 huyn; mi huyn c bnh qun l 21 x, mi x c bnh qun l 300 h. Nu theo phng php iu tra chn mu n gin, phi lp danh sch ca tng s l: 12x 21x 300 = 75.600 h. Nu dng phng php iu tra chn mu phn tng v c tng s l 3 tng: tng th nht l chn huyn (chn 1/2 s huyn); tng th hai l chn x (mi huyn chn 1/3 s x) va tng th ba l chn h (mi x chn iu tra 30 h) vic lp khung chn mu cp 1 v cp 2 rt dP v danh sch cc huyn ca mt tnh, cc x ca mt huyn lun c sn ch cn lp danh sch cc h 42 x ch khng phi l 252 x nh iu tra theo phng php chn mu ngu nhin n gin.

Nh vy l khi lng cng vic ch cn khong 1 phn 5 khi lng cng vic ca cc cuc iu tra thng thng.

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Ngu nhin

H thng

Phn lp

So snh 3 kiu ly mu3-12

Chng 3. THU THP, X L S LIU NGHIN CU3.1.5. L y m u ch tiu Qun th nghin cu c phn nhm hoc phn lp nh cch chn mu phn lp. i tng nghin cu trong mi nhm c ly mu theo t l bit v sau tin hnh phng php chn mu khng xc sut. Ngi nghin cu cn phi bit t nht cc s liu, thng tin trong qun th mc tiu phn chia cc ch tiu mun kim sot. V d: Phng vn bit c thc trng hot ng du lch thnh ph, X. Nghin cu trc y cho bit l do khch du lch ti thnh ph, gm: 60% nghi mt; 20% thm ngi thn; 15% kinh doanh v 5% hi hp. D tnh c mu mun phng vn l 500 khch du lch; chn nhng ni c nhiu khch du lch nh khch sn, khu vui chi gii tr, T l mu mun phng vn t c cho mi l do (ch tiu) nu trn s tng ng l 300, 100, 75 v 25 khc. Nu nh ch tiu 300 khch du lch n vi l do vui chi, gii tr c tr li cha th phi tip tc phng vn cho ti khi t c ch tiu.

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Thun li ca ly mu ch tiu: chi ph thc hin nghin cu tng i r v d (do khng cn phi thit lp khung mu). Bt li ca ly mu ch tiu: khng i din ton b qun th, do ly mu khng xc sut nh chn u tin phng vn khch du lch n trc, chn ni c nhiu khch lui ti, khch khch sn, .. Chn mu ch tiu t c p dng trong cc nghin cu pht trin, nhng i khi oc s dng trong mt vi nghin cu nh mang cc c tnh quan st. 3-14


3.1.6. c tnh c m u Mc ch c tnh c mu l gim i cng lao ng v chi ph lm th nghim nhng khng lm mt i cc c tnh ca mu v tin cy ca s liu i din cho qun th. Chn c mu qu ln hoc ln hn mc ti thiu th tn km cn chn cP mu di mc ti thiu li t chnh xc.3-15

Chng 3. THU THP, X L S LIU NGHIN CU c tnh cP mu cho mt gia, tr trung bnh Vi gia thit ly mu ngu nhin va cP mu u ln c phn b, 2 chun:

z / 2 n= E

E: sai s mong mun Z/2: gi tr ngng ca phn b chun (bng) n : c mu : lch chun qun th Nu c mu n < 30, chng ta c th tnh t lch chun mu s. Ngoi ra cng c th tnh t nhng qun th tng t hoc t th nghim th im

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Chng 3. THU THP, X L S LIU NGHIN CUV d 1: Mt nghin cu mun xc nh nng trung bnh ca mt cht nhim ti mt v tr quan trc. Kho st s b 10 mu i din cho cc gia, tr nng l 291,320, 140, 223, 219, 195, 248, 251, 163, va 292 mg/L. Hi cn bao nhiu mu c lng nng cht nhim vi sai s, 20 mg/L vi khong tin cy 95%? Gia, tr TB ca 10 mu = 234.2 mg/L va lch chun mu s = 58.0 mg/L Khong tin cy 95% ca c lng tnh c vi t9,0.025 = 2.228 l:

tc gia, tr thc nm gia 193 va 275 mg/L. S, mu cn gia, tr thc c c lng vi sai s, 20 mg/L:

z s 1,96 58 n = /2 = = 32 E 20 2 2

aP c 10 mu c thc hin, vy cn thm 22 mu na.3-17

Chng 3. THU THP, X L S LIU NGHIN CU V d 2: Mt ti mun nh gi hm lng trung bnh ca P trong mt h. Mt nghin cu nhiu nm trc cho lch chun qun th = 1,5 mg/L. Bao nhiu mu nc cn c ly o hm lng P chnh xc m 95% mu c c sai s khng vt qu 0,2 mg/L? z / 2 1,96 1,5 n= = 216 = E 0,2 2 2

Nh vy, ngi nghin cu cn ly 216 mu nc phn tch c hm lng trung bnh ca phosphorus trong h vi sai s khng qu 0,2 mg/L.3-18

Chng 3. THU THP, X L S LIU NGHIN CU3.2. Phng php phi thc nghim 3.2.1. Khi ni m

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Chng 3. THU THP, X L S LIU NGHIN CU3.2.2. Ph ng php ph ng v n-tra l i

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Chng 3. THU THP, X L S LIU NGHIN CU(1). Ph ng v n c nhn

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Chng 3. THU THP, X L S LIU NGHIN CU(1). Ph ng v n c nhn

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Chng 3. THU THP, X L S LIU NGHIN CU(2). Ph ng v n nhm m#c tiu hay nhm trung tm

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Chng 3. THU THP, X L S LIU NGHIN CU3.2.3. Ph ng php s d#ng b ng cu h i (Questionnaire)

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Chng 3. THU THP, X L S LIU NGHIN CU Cc m u cu h i

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Chng 3. THU THP, X L S LIU NGHIN CU Mt s cch ci tin mc tr li cu hi qua nghin cu s dng bng cu hi

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Chng 3. THU THP, X L S LIU NGHIN CU 3.3. Phng php thc nghim 3.3.1. Khi ni m

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3.3.2. Cc lo(i bi)n trong thi* nghi m

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Chng 3. THU THP, X L S LIU NGHIN CU3.3.3. Ph ng php quy ho(ch thi* nghi m (thi)t k* TN) Bi ton: khi kho st nh hng ca cc yu t, n 1 qu trnh, lm th, no xc nh iu kin ca mi yu t, qu trnh ti u? Cch lm thng thng: mi ln thay i 1 yu t, trong khi c, nh cc yu t, khc (COST: Change One Separate factor at a Time) V d: Kho st nh hng pH, tc khuy (v), liu keo tu (c) n hiu qu keo tu, lm cc thi, nghim: GiP v = 200 rpm, c = 100 mg/L, thay i 5 mc pH: 4, 5, 6, 7 va 8 (5 thi, nghim) hiu qu tt nht pH = 6 GiP pH = 6, v = 200 rpm, thay i 5 liu keo tu: 25, 50, 75, 100 va 125 mg/L (5 thi, nghim) hiu qu tt nht liu 75 mg/L GiP pH = 6, c = 75 mg/L, thay i 5 mc tc khuy: 100, 150, 200, 250 va 300 rpm (5 thi, nghim) hiu qu tt nht 250 rpm Kt qu chung: lm 15 thi, nghim, kt lun keo tu ti u pH = 6, c = 75 mg/L va v = 250 rpm3-35

Chng 3. THU THP, X L S LIU NGHIN CU Hn ch, ca COST: - S, TN tin hnh nhiu - Khng cho bit thng tin khi cc yu t, thay i ng thi (tc bo qua s tng tc gia cc yu t,) - iu kin tm thy cha phi l ti u: v d, bit u pH = 5, c = 75 mg/L va v = 200 rpm cho hiu qu tt hn? mun kim tra ht cc t hp iu kin phi lm 53 = 125 thi, nghim! (tng qut N = lk thi, nghim vi l: s, mc thay i, k: s, yu t,)3-36

Chng 3. THU THP, X L S LIU NGHIN CUThit k* thi* nghim (Design of Experiment = DOE ) Mi yu t, c 3 mc thay i: mc TB (gia, tr xut pht), mc cao (tng ln vi 1 gia s, xc nh) va mc thp (gim i ng vi 1 gia s,) M ha cc yu t, cc mc ng vi gia, tr 0, -1 va +1 V d:Yu t T pH c, mg/L v, rpm Mc thp 5 50 150 Mc TB 6 75 200 Mc cao 7 100 250 M ha X1 X2 X3 -1 -1 -1 Mc 0 0 0 +1 +1 +1

pH 6 X1 = 1

c 75 X2 = 25

X3 =

v 200 503-37

Chng 3. THU THP, X L S LIU NGHIN CUThi)t k* y u (full factorial design)- S, thi, nghim N = 2k + 3 (3 l s TN lp li mc trung tm c lng sai s) - Vi v d trn, N = 23 + 3 = 11 thi, nghim theo bng k, hoch:TN s, 1 2 3 4 5 6 7 8 9 10 11 X1 +1 +1 +1 +1 -1 -1 -1 -1 0 0 0 X2 +1 +1 -1 -1 +1 +1 -1 -1 0 0 0 X3 +1 -1 -1 +1 +1 -1 -1 +1 0 0 03-38

Yi

Chng 3. THU THP, X L S LIU NGHIN CU Tin hnh cc thi, nghim theo mt trnh t ngu nhin; ghi nhn cc kt qu (Yi, i = 1 n N) Xy dng m hnh hi quy a bin, v d: Y = b0 + b1X1 + b2X2 + b3X3 + b12X1X2 + b13X1X3 + b23X2X3 + b123X1X2X3 nh gia, mc nh hng ca mi yu t,, tng tc gia cc yu t, thng qua gia, tr va du cc h s, b1, b2,,b12,..., b123 Biu din thi mt cong, xc nh im ti u tnh va cc gia, tr tng ng ca X1, X2, X3 cc gia, tr thc ca cc yu t, iu kin ti u3-39


Thi)t k* khng y u (fractional factorial design) - Khi s, yu t, nhiu hn 5, s, TN nu thit k, y u s rt ln c th thit k, mt phn gim m khng gim nhiu thng tin. - S, thi, nghim N = 2k-p + 3

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Chng 3. THU THP, X L S LIU NGHIN CU3.4. X+ ly* va trnh by s* liu 3.4.1. X ly* th ng k n gi n ph bi)n Tnh gia, tr trung bnh Trung bnh cng (arithmetic mean): a s, trng hp Trung bnh nhn (geometric mean): khi gia, tr s, o khc nhau cP s, m (10x, ex), v d mt vi khun

Tnh lch chun (s = standard deviation): phn nh s bin thin ca cc c th trong qun th mu Tnh sai s, chun (SE = standard error): phn nh s bin thin ca cc gia, tr trung bnh mu chn t qun th mu Xc nh cc c trng thng k khc: min, max, trung v (median) Xem chi tit hc phn Thng k mi trng3-41

Chng 3. THU THP, X L S LIU NGHIN CU Thng dng va n gin nht tnh cc thng s, thng k l s dng MS Excel V d 1. X ly, thng k n gin mt phn kt qu iu tra bng phiu cu hi 3 xaP in Lc (Phong in), Qung Ngn va Qung Tho (Qung in) lin quan n s, nhn khu trong h va thu nhp hng thng ca cc h. Xem file excel.Bng 3.2. Kt qu iu tra s, nhn khu va thu nhp h gia nh 3 xaP XaP S, h iu tra (n) S, khu/h, TB s Thu nhp, x1000 ng/h/thng in Lc 57 3,7 1,5 2714,91 1797,37 Qung Ngn 55 4,9 1,4 2678,18 1594,52 Qung Tho 51 4,0 1,3 2327,45 1348,203-42

Chng 3. THU THP, X L S LIU NGHIN CU 3.4.2. Cc tnh ton th ng k +c bi t Phn tch tng quan H s, tng quan r

Phn tch hi quy

V d: tng quan BOD5 va COD mu nc (slide)

Hi quy tuyn tnh, phi tuyn tnh V d: xy dng ng chun hi quy tuyn tnh y = ax + b a: h s, gc b: on ct trc tung h s, hi quy r (tng t h s, tng quan)3-43

Chng 3. THU THP, X L S LIU NGHIN CU V d: tng quan BOD5 va CODCOD 9.1 15.8 10.9 9.9 8.3 8.1 12.1 10.2 10.1 9.4 8.1 9.7 7.9 11.1 7.6 8.5 8.6 7.8 7.2 8.5 BOD5 4.5 7.2 5.0 4.3 4.7 4.2 4.8 4.7 4.1 5.2 4.9 5.0 5.3 5.4 4.4 4.9 5.5 3.5 4.3 3.8 COD 7.0 6.2 7.1 10.0 10.1 17.5 16.0 11.2 9.6 10.3 7.9 13.1 9.2 5.7 16.5 12.5 12.0 14.6 12.8 9.5 BOD5 3.1 3.9 4.5 5.2 5.9 8.2 8.3 6.9 5.1 4.1 4.9 6.4 5.2 4.0 7.5 5.1 4.6 6.0 5.6 5.4

1. Dng hm CORREL(array1, array2) trc tip nhn c R = 0,83 2. Dng Tools >> Data Analysis >> Correlation nhn c R = 0,83 3. Dng thi: Add trendline h s, R2 = 0,69 >> Linear R = 0,83

Xem file excel3-44

Chng 3. THU THP, X L S LIU NGHIN CUV d: Xy dng ng chun xc nh NH4-N theo PP trc quangD.d chun NH4+ C, mg-N/L Abs 1 0 0.008 2 0.15 0.215 3 0.3 0.412 4 0.45 0.678 5 0.6 0.82

1. Phng php veP thi 2. Phng php tnh trc tip cc h s, 3. Kt qu: H s, gc a = 1,3913 on ct trc tung b = 0,0092 Phng trnh ng chun: Abs = 1,3913*C + 0,0092

y = 1.3913x + 0.0092 1.0 0.8 0.6 0.4 0.2 0.0 0.00 0.15 0.30 C, mg-N/L 0.45 0.60 R = 0.9942

Abs

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