### Sample size calculation : Comparative studies

**When case data is on nominal/ordinal scale and proportion is parameter of the study**

n = [p

_{1 }(1-p_{1}) + p_{2}(1 - p_{2})] / (p_{1 - }p_{2})^{2}* Cn = Minimum sample size for a group

p1
and p2
= Proportion of two groups

C = Standard value for the corresponding level of α and β
selected for the study:

- 80% power and 95% CI = 7.85
- 90% power and 95% CI = 10.51
- 80% power and 99% CI = 11.68
- 90% power and 99% CI = 14.88

**When case data is on interval/ratio scale and mean is parameter of the study**

n = [σ

_{1}^{2}+ σ_{2}^{2}] (Z_{1-b}+ Z_{1-a/2})^{2}/ d^{2}^{}

d = difference in means of two group (effect size)

σ1
= SD of Group 1

σ2 = SD of Group 2

Z

_{1-b}= Desired power (0.84 for 80% power and 1.282 for 90% power)Z

_{1-a/2 }= Critical value and a standard value for the corresponding level of confidence (1.96 at 95% CI and and 2.58 at 99% CI)**Reference:**http://njppp.com/fulltext/28-1567942207.pdf

Epomedicine Thesis Help

MD, MS, PhD Thesis, Proposal and Medical Research Guide from Epomedicine - Word formatting, Sample size calculation, Referencing, Reference manager and Calculators.

Epomedicine July 04, 2020

A researcher wants to compare the knowledge among Group A and Group B. From the previous study, proportion of the two groups is taken, i.e., 40% and 20%, respectively. A researcher wants 95% CI and 80% power for the study. Calculate the total subjects required for a new study.

p1 = 0.4

p2 = 0.2

C = 7.85

From calculation, n = 79 in each group

Epomedicine July 04, 2020

Assuming from the previous study that the mean (SD) of HbA1 c level in Group A and Group B was 5.5 (2.2) and 7.5 (2.0), respectively. At 95% CI and 80% power of the study, find out the sample size for the new study,

σ1 = 2.2

σ2 = 2

d = 7.5-5.5 = 2

From calculation, n = 153 in each group