How to find sample size for Two Independent Samples Groups: If Variable Measured on Nominal scale.
The sample size is calculated using following Formula
Source:
Lwanga SK, Lames haw S. Sample size determination in health studies. WHO, Geneva, 1991.
Where:
| n | Sample size. |
| Z1 | Value for the selected alpha level (1.96 at 95% confidence level). |
| Z2 | value associated with selected Power (0.84 at 80% power of test). |
| P1 | Probability of variable in sample-One (Value <1 .0=""> |
| P2 | Probability of variable in sample-Two (Value <1 .0=""> |
| P | Average of P1 and P2. |
Example:
Suppose if we have to conduct a study for two independent groups. For estimating difference between amenia levels in school going girls and boys for calculation of sample size sufficient liturature is not available so pilot study was conducted and findings of pilot study shows that 18% girls and 12% boys suffered from anemia. Here we considered 95% confidence level and 80% power of test. What will be the minimum sample size for both the groups?
| P1 | Probability of variable in sample-One (Value <1 .0=""> | 0.18. |
| P2 | Probability of variable in sample-Two (Value <1 .0=""> | 0.12. |
| P | Average of P1 and P2 (0.18+0.12=0.30/2). | 0.15 |
| Z1 | value for 95% confidence level | 1.96. |
| Z2 | value for 90% power of test | 0.84. |
By putting the values in above formula
n = 555
Required sample size for study is 555 subjects in each group.
So we will enrol 555 subjects in Group-I and 555 subjects Group II.
