Hi Statalisters,
a Dentistry PhD student did some measurements on 12
teeth with varying conditions and he asked me how
could he show that the device used for the
measurements is reliable. More specifically each one
of the 12 teeth has been measured by this device by 2
raters (a and b) X 2 time points (week 1 and week 2) X
6 relative positions = 24 measurements. The goal is
to show that the discrepancies among measurements are
not statistically significant.
My first thought was to use a 2-level model
(measurements nested within tooth) and test the rater,
time, position effects and maybe their interractions.
Something like
xi:xtreg length i.rater i.time i.position,i(tooth)
assuming that a random intercept structure is adequate
for this experiment.
The problem is that this is the first time I deal with
a problem where the goal is to "prove" that some
factors have no significant effects, thus I am not
very confident with the aforementioned method.
Any thoughts?
Nikos Pantazis
Biostatistician
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