I have done a three way ANCOVA in R. I am testing how temperature, the development stage and the size of a carcass affect the development rate of maggots.
My response variable is Duration
(a measurement of hours) and my factors are Size
(2 levels = small and large), and Stage
(7 levels = eggs, 1st instar, 2nd instar, 3rd instar, postfeed, pupa and total) and Temperature
(4 levels = 15, 20, 25, 30). Size
and Stage
are fixed factors. However, Temperature
is a continuous factor (I am analysing it as a covariate).
My function is:
Duration1 <-(aov(Duration~Stage*Temperature*Size, ThreeWayDuration))
summary(Duration1)
This gave me:
Df Sum Sq Mean Sq F value Pr(>F)
Stage 6 7206782 1201130 149.059 < 2e-16 ***
Temperature 1 1924926 1924926 238.881 < 2e-16 ***
Size 1 78491 78491 9.741 0.00205 **
Stage:Temperature 6 2500293 416716 51.714 < 2e-16 ***
Stage:Size 6 120539 20090 2.493 0.02367 *
Temperature:Size 1 140090 140090 17.385 4.43e-05 ***
Stage:Temperature:Size 6 184679 30780 3.820 0.00122 **
Residuals 214 1724431 8058
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
I want to do post hoc tests. I know I do not need a post hoc test for Size
because it only has two levels.
I have used the TukeyHSD () function for Stage
:
TukeyHSD(Duration1, "Stage")
This gave the diff, lwr, upr, and p adj values for each interaction. However there is a warning message:
Warning messages:
1: In replications(paste("~", xx), data = mf) :
non-factors ignored: Temperature
2: In replications(paste("~", xx), data = mf) :
non-factors ignored: Stage, Temperature
3: In replications(paste("~", xx), data = mf) :
non-factors ignored: Temperature, Size
4: In replications(paste("~", xx), data = mf) :
non-factors ignored: Stage, Temperature, Size
What does this mean? With these warnings has it given me the correct values?
I also understand that the Tukey test only works for categorical factors.
What post hoc test can I use to examine Temperature
in R, as this is a continuous factor?
Many thanks
Stage
when there should be 6. Fix that problem first. $\endgroup$