# R/indt.R In pwr2ppl: Power Analyses for Common Designs (Power to the People)

#### Documented in indt

#'Compute power for an Independent Samples t-test
#'Takes means, sds, and sample sizes for each group. Alpha is .05 by default, alternative values may be entered by user
#'@param m1 Mean of first group
#'@param m2 Mean of second group
#'@param s1 Standard deviation of first group
#'@param s2 Standard deviation of second group
#'@param n1 Sample size for first group
#'@param n2 Sample size for second group
#'@param alpha Type I error (default is .05)
#'@examples
#'indt(m1=22,m2=20,s1=5,s2=5,n1=99,n2=99)
#'indt(m1=1.3, m2=0, s1=4,s2=1,n1=78,n2=234)
#'@return Power for Independent Samples t-test
#'@export
#'
#'
indt<-function(m1=NULL,m2=NULL, s1=NULL,s2=NULL, n1=NULL,n2=NULL, alpha=.05){
x<-stats::rnorm(n1,m1,s1)
X<-x
MEAN<-m1
SD<-s1
Z <- (((X - mean(X, na.rm = TRUE))/stats::sd(X, na.rm = TRUE))) * SD
y<-MEAN + Z
group<-rep("A1",n1)
l1<-data.frame(y, group)
x<-stats::rnorm(n2,m2,s2)
X<-x
MEAN<-m2
SD<-s2
Z <- (((X - mean(X, na.rm = TRUE))/stats::sd(X, na.rm = TRUE))) * SD
y<-MEAN + Z
group<-rep("A2",n2)
l2<-data.frame(y, group)
simdat<-rbind(l1,l2)
anova<-stats::aov(y~group, data=simdat)
anova<-car::Anova(anova, type="III")
SSA<-anova[2,1] #column, row
SSwin<-anova[3,1]
dfwin<-anova[3,2]
mswin<-SSwin/dfwin
dfbg<-anova[2,2]
eta2<-SSA/(SSA+SSwin)
f2<-eta2/(1-eta2)
lambda<-f2*dfwin
d<-round((m1-m2)/(mswin^.5),3)
minusalpha<-1-alpha
Ft<-stats::qf(minusalpha, dfbg, dfwin)
Power<-1-stats::pf(Ft, dfbg,dfwin,lambda)
sx1_un <- s1/(n1^.5)
sx2_un <- s2/(n2^.5)
sx1x2_un <- ((sx1_un^2)+(sx2_un^2))^.5
t_un <- (m1-m2)/sx1x2_un
d_un <- round(t_un * sqrt((n1+n2)/(n1*n2)),3)
n_harm <- ((2*n1*n2)/(n1+n2))
var1<-s1^2
var2<-s2^2
sat_num <- ((var1/n1)+(var2/n2))*((var1/n1)+(var2/n2))
sat_denom <- ((((s1^2/n1)^2))/(n1-1)) +((((s2^2/n2)^2))/(n2-1))
df_un <- round(sat_num/sat_denom,3)
delta_un <-(d_un*((n_harm/2)^.5))
lambda_un <-delta_un^2
Ft_un<-stats::qf(minusalpha, dfbg, df_un)
Power_unequal<-1-stats::pf(Ft_un, dfbg,df_un,lambda_un)
pe<-round(Power,3)
pu<-round(Power_unequal,3)
message("Equal Variance Power for n1 = ",n1," ,n2 = ",n2, " with d = ", d, " = ", pe)
message("Unequal Variance Power for n1 = ",n1,"," ," n2 = ",n2, ", with d = ", d_un, " = ", pu)
result <- data.frame(matrix(ncol = 5))
colnames(result) <- c("n1", "n2","d","Power Equal Vars","Power Unequal Vars")
result[, 1]<-n1
result[, 2]<-n1
result[, 3]<-d
result[, 4]<-pe
result[, 5]<-pu
output<-na.omit(result)
rownames(output)<- c()
invisible(output)
}

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pwr2ppl documentation built on Sept. 6, 2022, 5:06 p.m.