Rent for Land Planted to Alfalfa

Keywords: multiple regression, variance modelling.

Description

The data were collected to study the variation in rent paid in 1977 for agricultural land planted to alfalfa in Minnesota. The data include:


Variable		Description

Rent		average rent per acre planted to alfalfa
AllRent		average rent paid for all tillable land
Cows		density of diary cows (number per square mile)
Pasture		proportion of farmland used as pasture
Liming		Yes if liming is required to grow alfalfa; No otherwise

Sanford Weisberg writes:

The unit of analysis is a county in Minnesota; the 67 counties with appreciable rented farmland are included.

Alfalfa is a high protein crop that is suitable feed for dairy cows. It is thought that rent for land planted to alfalfa relative to rent for other agricultural purposes would be higher in areas with a high density of dairy cows and rents would be lower in counties where liming is required, since that would mean additional expense.

Download

Data File (tab-delimited text)

Source

Weisberg, S. (1985). Applied Linear Regression. Wiley, New York. Problem 6.5. Douglas Tiffany is cited as the original source.

Analysis

wpe35.gif (4210 bytes)

A log-scale is needed for Rent and AllRent.
A square-root or similar scale is needed for Cows.
The ratio of Rent to AllRent increases with the density of cows, but flattens off for more than about 20 per square mile.
The counties where liming is required are predominatedly those with more than 20 cows per square mile.
The variance of log(Rent/AllRent) is appears to be greater when liming is required and there are more than 20 per square mile.