Bioequivalence and Bioavailability Forum

Dear Helmut,

Nope, no "true" initial concentration available (just 3 replicates prior first freezing step).

I thought on linear regression and test the slope to be different for zero. However, I do not like this approach for obvious reasons . Another approach may be to calculate the 95% CI for the mean at step 0 (kind of plausibility interval) and check if CI for the model-predictions is within that interval.

What do you think?

Best regards

PS.: Here is an artificial data set for illustration

# generate example data #
set.seed(54757)
step <- c(rep(0,3),rep(1,3), rep(2,3), rep(3,3), rep(4,3), rep(5,3))
x <- rnorm(n=length(step), mean=0, sd=1)
data <- data.frame(lot='Lot 1', step=step, x=x)

# linear regression #
mod <- lm(x ~step, data=data)
ci95 <- t.test(subset(data, step==0)$x)$conf.int
plot(x ~ step, data=data, ylim=c(-4, 4))
for(i in 1:3){points(predict(mod, interval='confidence')[,i]~data$step, type='l')}
abline(h=ci95, lty=3)