R/power.casectl.plot.R

In genetics: Population Genetics

power.casectrl.plot <- function (N, gamma=1.6, p=1:9/10, kp=0.1, alpha=0.05, fc=0.5,
                                 minh=c('multiplicative', 'dominant','recessive'),
                                 Nsnp=1, vary=c('prevalence','SNPs'), ylim=c(0,1), PLOT=T, ... )
{
  minh <- match.arg(minh)
  vary <- match.arg(vary)
  if (length(p)<2) stop('Must have more than 1 value in p.')
  if (length(kp) > 1 & length(Nsnp) > 1) stop("Nsnps and kp can't be all > 1.")
  if (vary=='prevalence') {
    cmd <- expression(tapply(p, p, function(x, ...) power.casectrl(p=x,...), N=N, gamma=gamma, kp=kp[j], alpha=alpha/Nsnp, fc=fc, minh=minh))
    Xvary <- kp 
  } else if (vary=='SNPs') {
    cmd <- expression(tapply(p, p, function(x, ...) power.casectrl(p=x,...), N=N, gamma=gamma, kp=kp, alpha=alpha/Nsnp[j], fc=fc, minh=minh))
    Xvary <- Nsnp 
  }
  J <- length(Xvary)
  ret <- matrix(NA, ncol=J, nrow=length(p))
  colnames(ret) <- paste(vary, '=', Xvary)
  for (j in 1:J) ret[,j] <- eval(cmd)

  if (PLOT) {
    nc <- 1:ncol(ret)
    subt <- paste("( RR", gamma, "; total subjects", N,"; SNPs", Nsnp[1], "; prevalence", kp[1],
                   "; mode of inheritance:", minh, "; overall sig.level", alpha, ")" )
    matplot(p, ret, type="l", ylim=ylim, lty=1, col=nc, xlab="Allele Frequency", ylab="Power", sub=subt, ...)
    abline(h=c(.8), lty=1)
    legend( locator(1), colnames(ret), lty=1, col=nc )
  }
  ret
}


### simple simulation for two group design
pw <- function(n1, n2=n1*(1-fc)/fc, fc=.5, pi=0, me1=50, me2=45, sd1=10, sd2=10, TEST=F){
  covm <- matrix(c(1,    pi,    pi,    1   ), nrow=2)*
          matrix(c(sd1^2, sd1*sd2, sd1*sd2, sd2^2), nrow=2)
  x1 <- rmvnorm(n=n1, mean=c(me1,me1), sigma=covm)
  x2 <- rmvnorm(n=n2, mean=c(me1,me2), sigma=covm)
  x <- data.frame(rbind(x1,x2), Trt=c(rep(0,n1), rep(1,n2)))
  colnames(x) <- c('X', 'Y', 'Trt')
  mod <- lm(Y~X+Trt, data=x)
  if (TEST) {
    print( summary(mod) )
    plot(Y~X+Trt, data=x)
  }
  ret <- anova(mod, test='F')['Trt','Pr(>F)']
  ret
}

# power calculation for studies using baseline measure 
#   - simulation: continuous response, baseline and genotype as covariate (ANCOVA)
#   - can specify various modes of inheritance ('additive', 'dominant','recessive')
#   - use compound symmetry for covariance matrix 
# Author: Michael Man
#   Date: June 22, 2004
#      N: total number of subjects
#      p: frequency of A allele
#  alpha: significance level                     (used only in 'power.genotype.conti')
#    Rep: number of iterations to generate power (used only in 'power.genotype.conti')
#     pi: correlation coefficient
#    me1: mean of control group
#  delta: treatment/genotype effect
#  sd1/2: standard deviation of the control and treatment groups
#   minh: mode of inheritance
# genotype.delta: the effect due to individual genotype effect or overall effect
# Factor: whether treat 'Trt' as a factor in 'x'
#   TEST: debug
# reference:
#   Frison and Pocock (1992) "Repeated measures in clinical trials: analysis using mean summary statistics
#     and its implications for design" Statistics in Medicine 11:1685-1704
#   Vickers (2001) "The use of percentage change from baseline as an outcome in a controlled trial is
#     statistically inefficient: a simulation study" BMC Med Res Methodol. 2001; 1 (1): 6
# requirement: need library 'mvtnorm'

simu.genotype.conti <- function (N, p=0.15, pi=0, me1=50, me2=me1, delta=-5, sd1=10, sd2=10, TEST=F,
                                minh=c('additive', 'dominant','recessive'), genotype.delta=T, Factor=F) 
{
  minh <- match.arg(minh)
  if ( min(N, sd1, sd2)<0 ) stop('N, sd1, and sd2 must be greater than 0')
  if ( p<=0 | abs(pi)<0 | p>=1 | abs(pi)>1 ) stop('p and abs(pi) must be between 0 and 1.') 
  f.mod <- switch(minh,
         dominant       = c(      0,     1, 1),
         additive       = c(      0 ,  0.5, 1),
         recessive      = c(      0,     0, 1)  ) 
  q <- 1 - p
  fhw <- c(q^2, 2*p*q, p^2)  # major allele first
  nhw <- round(N*fhw)
  if (sum(nhw)!=N) nhw[3] <- N-sum(nhw[1:2])
  covm <- matrix(c(1,    pi,    pi,    1   ), nrow=2)*
          matrix(c(sd1^2, sd1*sd2, sd1*sd2, sd2^2), nrow=2)
  if (!genotype.delta) delta <- delta/sum(fhw*f.mod)  # convert to overall delta due to all genotypes

  ## Give explicit variable definitions for variables created by the
  ## next loop to avoid unassigned variable message. 
  x1 <- x2 <- x3 <- t1 <- t2 <- t3 <- NULL 

  for (i in 1:3) {
    if (nhw[i]!=0) {
      assign(paste('x',i,sep=''), rmvnorm(n=nhw[i], mean=c(me1,me2+f.mod[i]*delta), sigma=covm))
      assign(paste('t',i,sep=''), rep(f.mod[i],nhw[i]))
    } else {
      assign(paste('x',i,sep=''), NULL)
      assign(paste('t',i,sep=''), NULL)
    }
  }
  x <- data.frame(rbind(x1,x2,x3), Trt=c(t1,t2,t3))
  if (Factor) x$Trt <- as.factor(x$Trt)
  colnames(x) <- c('X', 'Y', 'Trt')
  mod <- lm(Y~X+Trt, data=x)   # ANCOVA
  if (TEST) {
    print( summary(mod) )
    plot(Y~X+Trt, data=x)
  }
  ret <- anova(mod, test='F')['Trt','Pr(>F)']
  ret
}

### power calculation
power.genotype.conti <- function(N, Rep=100, alpha=.05, ...){
  pval <- sapply(rep(N, Rep), FUN=simu.genotype.conti, ...)
  power <- length(pval[pval<=alpha])/length(pval)
  power
}