Sample Size Calculator: Simple Logistic Regression

Hypothesis: Two-Sided Equality for continuous covariate



Data Input: (Help) (Example)

Input

 

Results

α

 

 

£]

 

P1

 

N

P2

 

 

Note:

Variables

Descriptions

£\

Probability of type I error

£]

Probability of type II error

P1

Event rate at X = 0

P2

Event rate at X = 1

N

Required sample size

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Application: This section illistrates how to determine the minimum sample size for simple logistic regression with a continuous covariate.

Procedure:

  1. Enter

a)    Value of £\, the two-sided confidence level

b)    Value of £], the type II error (1-power)

c)    Event rates

  1. Click the button ¡§Calculate¡¨ to obtain

a)    The required sample size.

  1. Click the button ¡§Reset¡¨ for a new calculation

Formulae:

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Example

Example 1: Given a design with high event rates P1=0.4 and P2=0.5, what is the required sample size for a simple logistic regression? (Assume both Type I and Type II error to be 0.05).

z£\/2=1.960

z1-£]=1.645

V(£]*)=0.92109

£]*=0.40547

£_=1.23999

N = 380

Therefore, 380 participant is required.


Example 2: Given a low prevalence rate P1=0.05 and P2=0.1, what is the required sample size for a simple logistic regression? (Assume both Type I and Type II error to be 0.05).

N =503

Therefore, 503 participant is required.

Reference: F.Hsieh, D.Bloch and M.Larsen. A Simple Method of Sample Size Calculation for Linear and Logistic Regression. Stanford, 1998. Print.

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