On 11/07/2013 07:46 AM, c_e_cressler wrote:
Hi,
The data (attached) I am looking at consists of measurements of growth rate
at different ages, for individuals in two treatments (control and infected).
What I want to know is whether and when (what age) the growth rate of
infected individuals is higher than the growth rate for control individuals.
The simplest way to approach this question is to just do a t-test at each
age, but because the growth rates at a given age depend on the growth rates
at previous ages before, that seems statistically invalid. I have looked at
some of the time series literature, but most of that seems more complicated
than what I am trying to do. What I would like to be able to say is
something like, "The growth rate of infected individuals is higher than
control individuals for ages 18-30."
Hi Clay,
If you calculate the mean growth rates:
inf_mean<-apply(as.matrix(inf.grates),1,
mean,na.rm=TRUE)
cntl_mean<-apply(as.matrix(cntl.grates),1,
mean,na.rm=TRUE)
and plot them:
plot(cntl_mean,col=3)
points(inf_mean,col=2)
It looks like the growth rate in the infected group is consistently
greater. Testing the linear models:
summary(lm(cntl_mean~I(1:length(cnf_mean))))
summary(lm(inf_mean~I(1:length(inf_mean))))
looks like there is a significant effect. The proper comparison would be
a mixed model with the individual scores, I think.
Jim
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