nDep2sam {PracTools}

Simple random sample size for difference in means

Description

Compute a simple random sample size for estimating the difference in means when samples overlap

Usage

nDep2sam(S2x, S2y, g, r, rho, alt, del, sig.level=0.05, pow=0.80)

Arguments

S2x

unit variance of analysis variable x in sample 1

S2y

unit variance of analysis variable y in sample 2

g

proportion of sample 1 that is in the overlap with sample 2

r

ratio of the size of sample 1 to that of sample 2

rho

unit-level correlation between x and y

alt

should the test be 1-sided or 2-sided; allowable values are alt="one.sided" or alt="two.sided".

del

size of the difference between the means to be detected

sig.level

significance level of the hypothesis test

pow

desired power of the test

Details

nDep2sam computes sample sizes in two groups that are required for testing whether the difference in group means is significant. The power of the test is one of the input parameters. The samples have a specified proportion of units in common. Both samples are assumed to be selected via simple random sampling.

Value

List with values:

n1

sample size in group 1

n2

sample size in group 2

S2x.S2y

unit variances in groups 1 and 2

delta

difference in group means to be detected

gamma

proportion of sample 1 that is in the overlap with sample 2

r

ratio of the size of sample 1 to that of sample 2

rho

unit-level correlation between analysis variables in groups 1 and 2

alt

type of test: one-sided or two-sided

sig.level

significance level of test

power

power of the test

Author(s)

Richard Valliant, Jill A. Dever, Frauke Kreuter

References

Valliant, R., Dever, J., Kreuter, F. (2018, chap. 4). Practical Tools for Designing and Weighting Survey Samples, 2nd edition. New York: Springer.

Woodward, M. (1992). Formulas for Sample Size, Power, and Minimum Detectable Relative Risk in Medical Studies. The Statistician, 41, 185-196.

See Also

nProp2sam

Examples

nDep2sam(S2x=200, S2y=200,
            g=0.75, r=1, rho=0.9,
            alt="one.sided", del=5,
            sig.level=0.05, pow=0.80)