ky thuat chon mau

7/28/2019 Ky Thuat Chon Mau

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Sampling TechniquesTran Van Hoang (MA.)


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Ths. Tran Van HoangChap 5-2

Cmau: 2

222/

zn

Trong o:- n: Son vcan ieu tra

- z/2 lahesotin cay c tra tbang

- : Sai socho phep

Xac nh c mau

Z tra t bng phn phi chun; hoc hm Excel: = NORMSINV(1-a/2)


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V du 1: Ngi ta tien hanh ieu tra chon mau e xac nh mc thu

nhap trung bnh trong nam cua cac ho gia nh nong dan vi yeu cau:

Sai so 20.000

o tin cay 95%.

o lech tieu chuan ve thu nhap c tnh la 160.000d.

24620

160.96,12

22

2

22

2/

z

n

Xac nh c mau


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2

2

2/ )1(

p

ppzn

Trong o:

P : Tyleca mu

z/2 lahesotin cay c tra tbang

p: sai socho phep

Xac nh c mau, c lng t l


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V du: iu tra v ty le cac ho dan tren a ban Tp HCM

co s dung tai khoan ngan hang vi yeu cau sai so 1%,o tin cay 95%, ty le mot cuoc khao sat th nghiem trc

o la 9%. Xac nh so ngi can ieu tra (n).

146.3

01,0

)91,0).(09,0(96,1)1(2

2

2

2

ppzn

Xac nh c mau


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Sampling techniques

Ths. Tran Van Hoang

Convenience

Samples

Non-Probability Samples

Judgement

Probability Samples

Simple

RandomSystematic

StratifiedCluster

Quota


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Probability sampling

Items of the sample are chosen basedon known or calculable probabilities

Ths. Tran Van Hoang

Probability Samples

SystematicStratified ClusterSimple random


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Chon mau ngau nhien n gianSimple Random Samples

Lp danh sch cc i tng v sp xptheo th t t 1 n N

La chn cc n v mu bng cch bc

thm, quay su im: Nhanh

Nhc im: Kh thc hin i vi cc

tng th lnVD: Lp danh sch cc DN XK go theo

th t ABC

Ths. Tran Van Hoang


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Ly mu h thngSystematic Samples

Lp danh sch cc i tng v sp xptheo th t t 1 n N

Xc nh c mu mun ly (n)

Xc nh khong cch chn mu (k)Trong k n v ngu nhin chn 1 mu,

cc mu tip theo ti v tr 2k, 3k

Ths. Tran Van Hoang


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Ly mu h thngSystematic Samples

VD: N=60, n=10, k = N/n=6Chon 1 so ngau nhien trong khoang 1-6, chang han chon c

so 4, ta se co cac n v mau la 4, 10,16,22,28, 34, 40, 46, 52, 58

Ths. Tran Van Hoang


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Ly mu theo khi (cm)Cluster Samples

Tng th c chia thnh cc khiChn ngu nhin cc khi iu tra

u im: gn nh, ph hp cho nhng

tng th c s n v ln, khng philp danh sch tng th m ch lpdanh sch khi

Nhc im: Sai s cao

Ths. Tran Van Hoang


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Ly mu theo khi (cm)Cluster Samples

V d: iu tra mc sng h gia nh trna bn thnh ph, kh lp danh sch cch gia nh, nhng c th lp danh sch

cc Phng, mi Phng c coi l 1khi.

Ths. Tran Van Hoang


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Ly mu phn tngStratified Samples

S dng khi cc i v khc nhau v tnhcht (Thu nhp, sinh vin cc kha)

Tng th c chia thnh cc tng

mi tng ny ly mu theo phngphp ly mu ngu nhin n gin haymu h thng

Do s n v mi tng l khc nhau nnc mu ly ra mi tng cng khc nhauda trn t l ca tng so vi tng th

Ths. Tran Van Hoang


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Ly mu phn tngStratified Samples

Ho to Ssinh vin % sinh vin Ssinh vin lyra tng tng

Chnh quy 10.000 50 500

Hon chnh 2.000 10 100

Bng 2 2.000 10 100

Tichc 5.000 25 250Cao hc 1.000 5 50

20.000 100 1.000

Ths. Tran Van Hoang


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Chn mu phi ngu nhinNon-probability sampling

Lay mau thuan tien (Convenient sampling)Lay mau nh mc (Quotasampling)Lay mau phan oan (Judgement sampling)

Ths. Tran Van Hoang


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Lay mau thuan tienConvenient sampling

Mau thuan tien c dung khi muon co mot c lng s bove ket qua ban quan tam ma khong muon mat nhieu thi gian

va chi ph

Co the lay mau thuan tien bang cach en nhng ni co kha

nang gap oi tng ieu tra thuan tien nhat theo thi gian,

hoan canh, a iem.

Ths. Tran Van Hoang


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Lay mau phan oanJudgement sampling

Trong lay mau phan oan, chung ta phai quyet nh e chonoi tng tham gia hp tac vao mau khao sat bang cac phan

oan cac oi tng thch hp e ieu tra.

Tnh ai dien cua mau khao sat thc te se phu thuoc nhieu

vao kien thc va kinh nghiem cua ngi nghien cu ieu tra,

kien thc va mc o hp tac cua oi tng ieu tra

Ths. Tran Van Hoang


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Lay mau nh mcQuota sampling

Lay mau nh mc tng t lay mau xac suat phan tang vtrc tien phai chia tong the thanh cac tang.

Trong tng tong the con, ngi phong van co the chon oi

tng ieu tra theo cach thuan tien hoac phan oan.

Ths. Tran Van Hoang


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Tham kho thm cc sildeting Anh bn di.

Ths. Tran Van Hoang


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Simple Random Samples

Every individual or item from thepopulation has an equal chance of

being selected

Selection may be with replacement orwithout replacement

Samples can be obtained from a table

of random numbers or computer

random number generators

Ths. Tran Van Hoang


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Business Statistics: A-

Chap 1-21

Simple Random Samples

Every individual or item from the

population has an equal chance of

being selected

Selection may be with replacement

or without replacement

Samples can be obtained from a

table of random numbers or

computer random number generators


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Stratified Samples

Population divided into subgroups

(calledstrata) according to somecommon characteristic

Simple random sample selected from

each subgroupSamples from subgroups are combined

into one

Ths. Tran Van Hoang

PopulationDividedinto 4strata

Sample


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Systematic Samples

Decide on sample size: nDivide frame ofN individuals into

groups ofk individuals: k=N/n

Randomly select one individual fromthe 1st group

Select every kth individual thereafter

Ths. Tran Van Hoang

N = 64

n = 8

k = 8First Group


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Cluster Samples

Population is divided into severalclusters, each representative of thepopulation

A simple random sample of clusters isselected All items in the selected clusters can be used, or items can be

chosen from a cluster using another probability sampling

technique

Ths. Tran Van Hoang

Population

divided into 16

clusters.

Randomly selected

clusters for sample


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C l i c k t o e d i t c o m p a n y s l o g a n .Xin cm n

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