Leaves for cauliflower plants at different times
Leaves for cauliflower plants at different times in two years.
A data frame with 14 observations on the following 4 variables.
yearyear factor
degdaysdegree days above 32F
leavesnumber of leaves
Numbers of leaves for 10 cauliflower plants in each of two years, and temperature degree-days above 32F, divided by 100.
The year is 1956-57 or 1957-58.
Over the data range shown, the number of leaves is increasing linearly. Extrapolating backwards shows that a linear model is inappropriate, and so a glm is used.
Roger Mead, Robert N Curnow, Anne M Hasted. 2002. Statistical Methods in Agriculture and Experimental Biology, 3rd ed. Chapman and Hall. Page 251.
Mick O'Neill. Regression & Generalized Linear (Mixed) Models. Statistical Advisory & Training Service Pty Ltd.
## Not run:
library(agridat)
data(mead.cauliflower)
dat <- mead.cauliflower
dat <- transform(dat, year=factor(year))
m1 <- glm(leaves ~ degdays + year, data=dat, family=poisson)
coef(m1)
## (Intercept) degdays year1957
## 3.49492453 0.08512651 0.21688760
dat$pred <- predict(m1, type="response")
libs(lattice)
libs(latticeExtra)
xyplot(leaves~degdays, data=dat, groups=year, type=c('p'),
auto.key=list(columns=2),
main="mead.cauliflower - observed (symbol) & fitted (line)",
xlab="degree days", ylab="Number of leaves", ) +
xyplot(pred~degdays, data=dat, groups=year, type=c('l'), col="black")
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