SDp_from_CIp {metaHelper}

Pooled Standard Deviation from Confidence Interval

Description

Computes the pooled standard deviation (e.g., standard deviation of an intervention effect) from confidence intervals and sample sizes. According to the Cochrane Handbook (see references), this standard deviation is referred to as the "within-group standard deviation." This method is valid only if the confidence interval is symmetrical around the mean and if either the t-distribution or normal distribution (when "t_dist = FALSE") was used to calculate the confidence interval.

Usage

SDp_from_CIp(
  CI_low,
  CI_up,
  n1,
  n2,
  sig_level = 0.05,
  two_sided = TRUE,
  t_dist = TRUE
)

Arguments

CI_low

lower limit confidence interval

CI_up

upper limit confidence interval

n1

sample size group 1

n2

sample size group 2

sig_level

significance level

two_sided

whether a two sided test for significance was used

t_dist

whether a t distribution has been used to calculate the CI

Value

Pooled standard deviation

References

Cochrane Handbook

See Also

SD_from_CI() for single group standard deviation.

Examples

#lower CI = 0.5, upper CI = 0.7, N1 = 50, N2 = 70
SDp_from_CIp(0.5, 0.7, 50, 70)