OPTIONS LS=75 PS=50;

/*
Analysis of Rates of Fatal Crashes (FC) on rural interstate highways
in New Mexico in the 5 years 1982-1986 (55 mph limit) and in
1987 (65 mph limit).

Data from JAMA by Gallaher et al. Oct. 27, 1989;262:2243-2245.

DATA:                 ---------- 55 mph -----------||-- 65 mph --

YEAR                 1982  1983  1984  1985  1986  ||   1987

Rates per100 million
vehicle miles*        2.8   2.0   2.1   1.7   1.9  ||    2.9

*vehicle miles; rate named "FC_Rate" below.

The aim is to take compare 1987 with the most relevant period;
the average of 1982-1986 is probably too high (rates seem to
have been falling over that time). Also one should take out the
systematic variation in the 5 years that, in the variance used
in the t-test or 1-way anova, appears as "unexplained noise".
In other words, the idea is to make the comparison both
FAIRER and SHARPER.

The authors fitted a regression line to the 5 years, calculated
the "expected" value for 1987 and the expected range of variation
around this fitted mean, and determine where, relative to this
predicted range of possible values, the observed value in 1987 lies.

*/

DATA sasuser.speedlim;

INPUT Year Limit FC_Rate;

LINES;
      1982   55    2.8
      1983   55    2.0
      1984   55    2.1
      1985   55    1.7
      1986   55    1.9
      1987   65    2.9
;
RUN;