How to find sample size based on Prevalence/ Incidence of a Disease.
For calculation of sample size in medical related studies wide number of software are available on internet. Using these open source/ paid softwares we can find sample size for a study based on Type of study (study design) and other Pre-requisites for calculation of sample size.
For Cross sectional Observational study design sample size can be calculated.
I] Prevalence/ Incidence of a disease.
II] Based on mean and Standard Deviation of parameter.
I] Based on Prevalence/ Incidence of a disease:
The sample size is calculated using following Formula
Source: Lwanga SK, Lameshaw S. Sample size determaination in health studies. WHO, Geneava, 1991.
Where:
| Symbol | Meaning |
|---|---|
| n | Sample size |
| Z² | Value for the selected alpha level (1.96 at 95% confidence level) |
| d | Desired level of precision |
| p | Prevalence or incidence of a disease |
| q | 1 - p |
Example 1: Suppose in an Observational study, we want to estimate Prevalence of Diabetic Mellitus disease. So how much population to be included in sample?
| Parameter | Symbol | Value | Explanation |
|---|---|---|---|
| Estimated Prevalence of Diabetes Mellitus in India | p | 0.10 | 10% |
| Complement of p | q | 0.90 | q = 1 - p = 1 - 0.10 = 0.90 |
| Confidence Level | Z | 1.96 | At 95% confidence level |
| Absolute Precision | d | 0.03 | 3% |
The sample size is calculated using following Formula
N = 384.16 = 384.
So required sample size for study is 384 samples.
Note: Sample size can be decrease by increasing precision of a study. Precision can consider up to prevalence or incidence.
