bssr.nb.inar1: Blinded Sample Size Reestimation for Longitudinal Count Data...
In spass: Study Planning and Adaptation of Sample Size

Description Usage Arguments Details Value Source See Also Examples

bssr.nb.inar1 fits blinded observations and recalculates the sample size required for proving a desired alternative when testing for a rate ratio between two groups unequal to one. See 'Details' for more information.

1	bssr.nb.inar1(alpha, power, delta, x, n, k)

`alpha`	level (type I error) to which the hypothesis is tested.
`power`	power (1 - type II error) to which an alternative should be proven.
`delta`	the rate ratio which is to be proven.
`x`	a matrix or data frame containing count data which is to be fitted. Columns correspond to time points, rows to observations.
`n`	a vector giving the sample size within the control group and the treatment group, respecitvely.
`k`	planned sample size allocation factor between groups: see 'Details'.

When testing for differences between rates μ_C and μ_T of two groups, a control and a treatment group respectively, we usually test for the ratio between the two rates, i.e. μ_T/μ_C = 1. The ratio of the two rates is refered to as δ, i.e. δ = μ_T/μ_C.

bssr.nb.inar1 gives back the required sample size for the control and treatment group required to prove an existing alternative theta with a specified power power when testing the null hypothesis H_0: μ_T/μ_C ≥ 1 to level alpha. Nuisance parameters are estimated through the blinded observations x, thus not further required.

for sample sizes n_C and n_T of the control and treatment group, respectively, the argument k is the desired sample size allocation factor at the end of the study, i.e. k = n_T/n_C.

rnbinom.inar1 returns the required sample size within the control group and treatment group.

rnbinom.inar1 uses code contributed by Thomas Asendorf.

rnbinom.inar1 for information on the NB-INAR(1) model, n.nb.inar1 for calculating initial sample size required when performing inference, fit.nb.inar1 for calculating initial parameters required when performing sample size estimation

#Calculate required sample size to find significant difference with
#80% probability when testing the Nullhypothesis H_0: mu_T/mu_C >= 1
#assuming the true effect delta is 0.8 and rate, size and correlation
#parameter in the control group are 2, 1 and 0.5, respectively.

estimate<-n.nb.inar1(alpha=0.025, power=0.8, delta=0.8, muC=2, size=1, rho=0.5, tp=7, k=1)

#Simulate data
placebo<-rnbinom.inar1(n=50, size=1, mu=2, rho=0.5, tp=7)
treatment<-rnbinom.inar1(n=50, size=1, mu=1.6, rho=0.5, tp=7)

#Blinded sample size reestimation
blinded.data<-rbind(placebo, treatment)[sample(1:100),]
estimate<-bssr.nb.inar1(alpha=0.025, power=0.8, delta=0.8, x=blinded.data, n=c(50,50), k=1)
summary(estimate)