Wemedoo Sample Size and Power Calculator

TEST FOR ONE PROPORTION

Purpose: To test for the number of subjects required to detect a significant difference between the sample proportion and a specific user-defined value.

Example: The aim of the study is to assess the proportion of patients with long term inflammation in patients that have developed resistance to semi-synthetic penicillin. Literature shows that 30% of patients on long term antibiotic therapy have developed resistance. In a specific population, it is assumed that resistance to semi-synthetic penicillin only 20%. A researcher wants to set up the study using the standard alpha of 0.05 (the probability of obtaining false positive result).

SAMPLE SIZE CALCULATION

How many subjects are sufficient to obtain a significant difference between the assumed proportion for the specific population and the proportion found in literature findings using 80% power?

Design:
Alpha (α) = 0.05
Power = 0.80
Proportion 1 = 0.2
Proportion 2 = 0.3

Result: A sample size of 153 subjects achieves 80% power to detect a significant difference between assumed proportion of patients in the specific population that have developed resistance to semi-synthetic penicillin and the proportion found in the literature.

POWER CALCULATION

What is the power achieved by examining 200 subjects in a study with the same proportions (30% vs 20%)?

Design:
Alpha (α) = 0.05
Sample Size (N) = 200
Proportion 1 = 0.2
Proportion 2 = 0.3

Result: Sample size of 200 subjects achieves a 90% power to detect a significant difference between the assumed sample proportion and that that found in the literature.