Description Usage Arguments Details Value Examples
prec_meandiff
returns the sample size or the precision for the
provided mean difference and standard deviations.
1 2 3 4 5 6 7 8 9 10 11  prec_meandiff(
delta,
sd1,
sd2 = sd1,
n1 = NULL,
r = 1,
conf.width = NULL,
conf.level = 0.95,
variance = c("equal", "unequal"),
...
)

delta 
difference in means between the two groups. 
sd1 
standard deviation in group 1. 
sd2 
standard deviation in group 2. 
n1 
number of patients in group 1. 
r 
allocation ratio (relative size of group 2 and group 1 (n2 / n1)). 
conf.width 
precision (the full width of the confidence interval). 
conf.level 
confidence level. 
variance 

... 
other options to uniroot (e.g. 
Exactly one of the parameters n
or conf.width
must be passed as NULL,
and that parameter is determined from the other.
Object of class "presize", a list of arguments (including the computed one) augmented with method and note elements.
1 2 3 4 5  # mean difference of 5, SD of 2.5, CI width with 20 participants assuming equal variances
prec_meandiff(delta = 5, sd1 = 2.5, n1 = 20, var = "equal")
# mean difference of 5, SD of 2.5, number of participants for a CI width of 3,
# assuming equal variances
prec_meandiff(delta = 5, sd1 = 2.5, conf.width = 3, var = "equal")

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