Story Name: Fish Prices
Datafile Name: Fish Prices
Abstract: The price of fish varies by species and time. The average price recieved by fishermen and vessel owners for several species of fish increased from 41 cents per pound in 1970 to $1.10 per pound in 1980. A paired t-test shows that this increase is highly significant.

There is a strong correlation (.967) between 1970 and 1980 prices. A scatterplot reveals that two species, lobsters and sea scallops, are outliers, but they follow the general trend of the rest of the data. One model that may be estimated from the data is a simple regression of 1980 price on 1970 price. However, a plot of the studentized residuals vs. 1970 price shows a cone-shaped pattern indicative of non-constant variance. Transforming both variables by taking the natural log results in a regression with high R-squared and F-ratio, and residuals with a constant variance.

Image: Plot of studentized residuals vs. 1970 price (untransformed model).

Image: Plot of studentized residuals vs. log(1970 price) (transformed model).