4. 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
5.
6. 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
7.
8. Multistage Sampling
•Sampling uses various techniques
•Population will be divided into
cluster, then into strata before the
sample will be taken
9.
10. 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-𝛼 of making an error no longer than d is given by the
following equation.
n=
𝑛0
1+ 𝑛0
𝑁
where n=sample size
N=Population size
𝑛0=estimation of sample requirement
11. Estimation of sample requirement
n=Z2 𝛼
2
(
𝑆2
d
2
)
Z2 =normal quantile cut off
𝛼
2
of the a for desired area of
normal distribution for desired accuracy
d= required precision that expresses how close to the
true mean the sample mean should be
𝑺2 = measure of variability
12. 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
𝛼
2
𝑆2
d
2
n=(1.96)2 (25)2
(10)2 =(1.96)2 575
100 =22.0892
n=
𝑛0
1+ 𝑛0
𝑁
n=
22.0892
1+22.0892
80
=17
