n.ttest {samplesize}

n.ttest computes sample size for paired and unpaired t-tests.

Description

n.ttest computes sample size for paired and unpaired t-tests. Design may be balanced or unbalanced. Homogeneous and heterogeneous variances are allowed.

Usage

n.ttest(power = 0.8, alpha = 0.05, mean.diff = 0.8, sd1 = 0.83, sd2 = sd1,
        k = 1, design = "unpaired", fraction = "balanced", variance = "equal")

Arguments

power

Power (1 - Type-II-error)

alpha

Two-sided Type-I-error

mean.diff

Expected mean difference

sd1

Standard deviation in group 1

sd2

Standard deviation in group 2

k

Sample fraction k

design

Type of design. May be paired or unpaired

fraction

Type of fraction. May be balanced or unbalanced

variance

Type of variance. May be homo- or heterogeneous

Value

Total sample size

Sample size for both groups together

Sample size group 1

Sample size in group 1

Sample size group 2

Sample size in group 2

Author(s)

Ralph Scherer

References

Bock J., Bestimmung des Stichprobenumfangs fuer biologische Experimente und kontrollierte klinische Studien. Oldenbourg 1998

Examples

n.ttest(power = 0.8, alpha = 0.05, mean.diff = 0.80, sd1 = 0.83, k = 1,
design = "unpaired", fraction = "balanced", variance = "equal")

n.ttest(power = 0.8, alpha = 0.05, mean.diff = 0.80, sd1 = 0.83, sd2 =
2.65, k = 0.7, design = "unpaired", fraction = "unbalanced", variance =
"unequal")