agridat (version 1.8.1)

ratkowsky.onions: Onion yields for different densities at two locations

Description

Onion yields for different densities at two locations

source

Ratkowsky, D. A. (1983). Nonlinear Regression Modeling: A Unified Practical Approach. New York: Marcel Dekker.

Details

Spanish white onions.

References

Ruppert, D., Wand, M.P. and Carroll, R.J. (2003). Semiparametric Regression. Cambridge University Press. http://stat.tamu.edu/~carroll/semiregbook/

Examples

dat <- ratkowsky.onions

# Model inverse yield as a quadratic.  Could be better...
library(lattice)
dat <- transform(dat, iyield = 1/yield)
xyplot(iyield ~ density, data=dat, group=loc, auto.key=TRUE)
m1 <- lm(iyield ~ I(density^2)*loc, dat)
dat$pred <- predict(m1)

require(latticeExtra)
xyplot(iyield ~ density, data=dat, group=loc, auto.key=TRUE) +
xyplot(pred ~ density, data=dat, group=loc, type='l')

# To do: semiparametric / gam model