A data set with the dry mass of all flowers and the dry mass of the total plant from 20 species growing at high and 20 species growing at low altitude.
A data frame with 40 observations on the following 3 variables.
a factor with levels
a numeric vector; dry mass of flowers in mg
a numeric vector; dry mass of total plant in mg
The data sets shows a random subsample of the original data set.
Fabbro, T. & Koerner, Ch. (2004): Altitudinal differences in flower traits and reproductive allocation. FLORA 199, 70-81. Fabbro, Koerner ()
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data(flowers) ## a model with two intercepts and two slopes # m1 <-lm(log(flower) ~ alt/log(total) -1, data=flowers) # ## a model with two intercepts and one slope # altdiff <- rbind("high-low"=c(1,-1)) # m2 <- lm(log(flower) ~ alt + log(total), data=flowers, # contrasts=list(alt=mycontr(contr=altdiff))) # ## are separate slopes needed? # anova(m1, m2) # conclusion: # ## no difference in slopes but difference in intercept ## for interpretation also test whether the slope is one!