R: Compute confidence limits for a difference of two independent...

ci.pd {Epi} | R Documentation

## Compute confidence limits for a difference of two independent proportions.

### Description

The usual formula for the c.i. of at difference of proportions is inaccurate. Newcombe has compared 11 methods and method 10 in his paper looks like a winner. It is implemented here.

### Usage

    ci.pd(aa, bb=NULL, cc=NULL, dd=NULL,
         method = "Nc",
          alpha = 0.05, conf.level=0.95,
         digits = 3,
          print = TRUE,
    detail.labs = FALSE )

### Arguments

`aa` | Numeric vector of successes in sample 1. Can also be a matrix or array (see details).
`bb` | Successes in sample 2.
`cc` | Failures in sample 1.
`dd` | Failures in sample 2.
`method` | Method to use for calculation of confidence interval, see "Details".
`alpha` | Significance level
`conf.level` | Confidence level
`print` | Should an account of the two by two table be printed.
`digits` | How many digits should the result be rounded to if printed.
`detail.labs` | Should the computing of probability differences be reported in the labels.

### Details

Implements method 10 from Newcombe(1998) (method="Nc") or from Agresti & Caffo(2000) (method="AC").

`aa`, `bb`, `cc` and `dd` can be vectors. If `aa` is a matrix, the elements `[1:2,1:2]` are used, with successes `aa[,1:2]`. If `aa` is a three-way table or array, the elements `aa[1:2,1:2,]` are used.

### Value

A matrix with three columns: probability difference, lower and upper limit. The number of rows equals the length of the vectors `aa`, `bb`, `cc` and `dd` or, if `aa` is a 3-way matrix, `dim(aa)[3]`.

### Author(s)

Bendix Carstensen, Esa Laara. http://bendixcarstensen.com

### References

RG Newcombe: Interval estimation for the difference between independent proportions. Comparison of eleven methods. Statistics in Medicine, 17, pp. 873-890, 1998.

A Agresti & B Caffo: Simple and effective confidence intervals for proportions and differences of proportions result from adding two successes and two failures. The American Statistician, 54(4), pp. 280-288, 2000.

### See Also

`twoby2`, `binom.test`

### Examples

    ( a <- matrix( sample( 10:40, 4 ), 2, 2 ) )
    ci.pd( a )
    twoby2( t(a) )
    prop.test( t(a) )
    ( A <- array( sample( 10:40, 20 ), dim=c(2,2,5) ) )
    ci.pd( A )
    ci.pd( A, detail.labs=TRUE, digits=3 )

[Package Epi version 2.44 Index]