# smd: Compute Standardized Mean Difference In smd: Compute Standardized Mean Differences

## Description

Computes the standardized mean differnce (SMD) between two groups.

d = √{D' S^{-1} D}

where D is a vector of differences between group 1 and 2 and S is the covariance matrix of these differences. If D is length 1, the result is multplied by sign(D).

In the case of a numeric or integer variable, this is equivalent to:

d = \frac{\bar{x}_1 - \bar{x}_2}{√{(s^2_1 + s^2_2)/2}}

where \bar{x}_g is the sample mean for group g and s^2_g is the sample variance.

For a logical or factor with only two levels, the equation above is \bar{x}_g = \hat{p}_g, i.e. the sample proportion and s^2_g = \hat{p}_g(1 - \hat{p}_g).

## Usage

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'character,ANY,missing' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'character,ANY,numeric' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'logical,ANY,missing' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'logical,ANY,numeric' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'matrix,ANY,missing' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'matrix,ANY,numeric' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'list,ANY,missing' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'list,ANY,numeric' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'data.frame,ANY,missing' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) ## S4 method for signature 'data.frame,ANY,numeric' smd(x, g, w, std.error = FALSE, na.rm = FALSE, gref = 1L) 

## Arguments

 x a vector or matrix of values g a vector of at least 2 groups to compare. This should coercable to a factor. w a vector of numeric weights (optional) std.error Logical indicator for computing standard errors using compute_smd_var. Defaults to FALSE. na.rm Remove NA values from x? Defaults to FALSE. gref an integer indicating which level of g to use as the reference group. Defaults to 1.

## Value

a data.frame containing standardized mean differences between levels of g for values of x. The data.frame contains the columns:

• term: the level being comparing to the reference level

• estimate: SMD estimates

• std.error: (if std.error = TRUE) SMD standard error estimates

## Examples

 1 2 3 x <- rnorm(100) g <- rep(1:2, each = 50) smd(x, g) 

smd documentation built on Oct. 23, 2020, 8:26 p.m.