stat chapte ix

Steven S. SolisMAHE-Ed Summer 2015

Statistical Methods in Education(Educ 242)

Sampling TechniquesContinuation

Sampling Techniques

Cont’n

Finding Sample Size

Sampling Techniques

Stratified Sampling Cluster Sampling

Multistage Sampling

Stratified Sampling• It is sampling technique ,simple random sampling and systematic sample are used hen the population is more o less homogenous•Hen studying a heterogeneous population a method of stratification is used.• Stratification- subdividing the population into

homogenous subgroups

Cluster Sampling•A process, the population is divided into large subgroups called clusters•Cluster sample is one of the units where random sample ill be taken•Usually it is by means of geographical situations

Multistage Sampling

•Sampling uses various techniques•Population will be divided into cluster, then into strata before the sample will be taken

Sample size

The part of the population that will represent the whole.The size of sample needed to estimate a population parameter with the probability 1- of making an error no longer than d is given by the following equation.

n= where n=sample sizeN=Population size

Estimation of sample requirement

n=Z2 )

Z2 =normal quantile cut offof the a for desired area of normal distribution for desired accuracyd= required precision that expresses how close to the true mean the sample mean should be

= measure of variability

Example:Given a population of 80 where the variance is 575 and a mean of 97.5 , how large should be the sample size so that probability will be 95% that the sample mean falls between +10 of the population mean? n=Z2 n=(1.96)2 =(1.96)2 =22.0892

n= n= =17

Variance is unknown(sloven)

n= where: n=sample sizeN=population sizee=desired margin of error

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Salamat!