What is sample size?
The sample size is define as the number of observations used
for determining the estimation of a given population.
Sample size means the number of observation or participants
included in the data collection/study. The sample should be of appropriate size
and representative of population being studied.
An adequate and appropriate sample size will ensure that
study/data collection will yield reliable information suggest the clinical and
non-clinical significance of the study.
For Calculating the sample size four basic component are
required
1.
P Value (or Alpha) : level
of significance we assume P<0.05 is significant. This type of error in
clinical research is also known as type 1 error or alpha. Type 1 error is inversely
proportional to sample size.
2. Power : Sometimes we may commit another type of
error where we may fail to detect the difference when actually there is the
difference. This is known as Type II error that detects false negative
results, exactly opposite to mentioned above where we find false positive
results when actually there was no difference. Type II error is the
probability of failing to find the difference between two study groups when
actually a difference exist and it is termed as beta (β). The
“power” of the study then is equal to (1-β)
and for a β of 0.2, the power
is 0.8, which is the minimum power required to accept the null hypothesis.
3. The
effect size: Effect size (ES) is the minimal difference
that need to detect between study groups. The difference between the value of the variable in the
control group and that in the test drug group is known as ES.
4.
The variability: The sample size calculation also
depend on population variance of given outcome variable, which is estimated by
the standard deviation. Sample size is directly proportional to SD, for e.g. in
homogeneous population SD will be low so as sample size require is low.
n=N/(1+Ne2)
(where n = number of sample, N= Total population and e =
Error tolerance)
By using 95% confidence level ( margin of error of 0.05)
|
Screening
population |
Sample size |
|
50 |
44 |
|
100 |
80 |
|
150 |
109 |
|
200 |
133 |
|
500 |
222 |
|
1000 |
286 |
|
2000 |
333 |
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