Hello R experts
I have two linear regressions for sexes (Male, Female, Unknown). All have a
good correlation between body length (response variable) and head length
(explanatory variable). I know it is not recommended, but for a good practical
reason (the purpose of study is to find a single conversion factor from head
length to body length), the regressions need to go through the origin (0
intercept).
Is it possible to do ANCOVA for these regressions without intercepts? When I do
summary(lm(body length ~ sex*head length))
this will include the intercepts as below
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) -6.49697 1.68497 -3.856 0.000118 ***
sexMale -9.39340 1.97760 -4.750 2.14e-06 ***
sexUnknown -1.33791 2.35453 -0.568 0.569927
head_length 7.12307 0.05503 129.443 < 2e-16 ***
sexMale:head_length 0.31631 0.06246 5.064 4.37e-07 ***
sexUnknown:head_length 0.19937 0.07022 2.839 0.004556 **
---
Is there any way I can remove the intercepts so that I can simply compare the
slopes with no intercept taken into account?
Thanks for help in advance.
Yusuke Fukuda
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