Sample Size Calculator: Matched/Paired Cohort


Data Input: (Help) (Example)

Input

 

Results

α

 

RR

£]

npairs

P0

 

 

P1

 

 

phi

 

 

 

Note:

Variables

Descriptions

£\

Probability of type I error

£]

Probability of type II error

P0

Proportion of the unexposed group

P1

Proportion of the exposed group

RR

Calculated Relative Risk

phi

Correlation coefficient given for a two by two table by the chi-square function.

npairs

Minimum number of cohort subject pairs

Help Aids Top

Application: This section illistrates how to determine the minimum sample size for paired cohort study. Matching in cohort study does not eliminate confounding. The control sample is not a random sample from the population and therefore population event rate is a poor estimate of p0 when confounders are strongly associated with the event.

Procedure:

  1. Enter

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

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

c)    Proportion for the unexposed group

d)    Proportion for the exposed group

e)    The ratio of unexposed to exposed

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

a)    The relative risk and required sample size pair

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

Formulae:

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Variable Notations:

α             The probability of type I error (significance level) is the probability of rejecting the true null hypothesis

β             The probability of type II error (1 - power of the test) is the probability of failing to reject the false null hypothesis.

P0            The proportion of the unexposed group

P1            The proportion of the exposed group

RR          The calculated relative risk

phi         Correlation (If not known from previous studies, it is better to assume 0.2 instead of independent)

Npairs      Minimum number of cohort subject pairs

Example

Reference:

Lemeshow, S., Hosmer Jr., D.W., Klar, J.,and Lwanga S.K. Adequacy of Sample Size in Health Studies. WHO, 1990. Print.

Dupont, W.D. Power calculations for matched casecontrol studies. Biometrics. 1988; 44: 1157¡V68.

Dupont, W.D. Power and sample size calculations. Controlled Clinical Trials. 1990; 11: 116¡V28.

Breslow, N.E. and Day, N.E. Statistical Methods in Cancer Research: The Analysis of Case-Control Studies. Lyon: International Agency for Research on Cancer, 1980.

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