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rstatisticslinear-regressionvarvariance
twilightecologist
twilightecologist

Reputation: 23

How to compare variance of distance between two treatments over time?

I am interested in understanding how my variable (distance) changes over time between two treatment groups. I now want to compare measures of variance for distance between the two treatment groups, but I am unsure the best way to go about this. Based on my figures, Treatment 1 has a slope of 0 and more variance, and Treatment 2 has a positive slope but I am not sure if variance increases over time for this group. What is the best way to test this? My data looks something like this:

Treatment Distance   Time
    1          7       2
    1          2       4
    1          3       1
    1          6       5
    2          2       2
    2          4       5
    2          6       8
    2          2       4

I can't take the variance of the residuals in a glmm yet, because this is preliminary analysis of a partial dataset and I don't have enough power. When I try to calculate a basic variance metric (not by time), I get NA.

var1<- var(Data$Distance[Data$Treatment == 1])
print(var1)
NA
var2<- var(Data$Distance[Data$Treatment == 2])
print(var2)
NA

Upvotes: 0

Views: 53

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