E.g. 9.1 

Predicting the interval to eruption of Old Faithful Geyser

A geyser is a hot spring that occasionally becomes unstable and 
erupts hot water and steam into the air. Different geysers will 
erupt for various lengths of time and intervals. Probably the most 
famous geyser is Old Faithful, in Yellowstone National Park, 
Wyoming. The intervals between eruptions of Old Faithful range 
from about 30 to 90 minutes. Water shoots to heights generally 
over 35 meters, with eruptions lasting  from 1 to 5.5 minutes 
(Marler, 1969). Because of its regularity and beauty,  Old 
Faithful Geyser is a major tourist attraction, and it is not 
uncommon  for several thousand people to watch an eruption on a 
summer  afternoon.   Prediction of the time of the next eruption 
of this geyser is of interest both to the Park Service and to 
visitors. In fact, prediction of the time of the next eruption is 
posted in prominent locations near the geyser. Given opposite are 
i = interval to the next eruption and dur = duration of an 
eruption, both in minutes, for all eruptions of Old Faithful 
Geyser  between 6 a.m. and midnight for August 1 (day=1) to August 8 
(day=8), 1978  Data on Old Faithful has been collected for many 
years by ranger naturalists in the park, using a stopwatch. The 
duration measurements  have been rounded to the nearest 0.1 
minutes or 6 seconds, while intervals are reported to the nearest 
minute. The National Park Service  uses values of x to predict 
future values for y, and we shall follow their  example. It is 
unlikely that a causal relationship exists between x and  y, 
rather both are probably results of some other unobserved cause or 
set of causes. Modeling the observed association between x and y 
may lead to useful predictions, but the fitted relationship may 
have no geological meaning.

Source: Weisberg, S. Applied Linear Regression, 2nd Edn. Wiley, 
New York, 1985.

Excerpts...

day interval   duration  year(1978=0, 1979=1)
1      78         4.4       0
1      74         3.9       0
1      68         4.0       0
..
..

8      77         4.2       0
8      73         4.4       0
..
8      80         4.8       0
8      79         4.1       0


Data for Validation:

119 eruptions of Old Faithful for the period August 16 to August 
23, 1979, a year after the original data.( in same format and same
dataset as above)


16     82         4.1       1
16     80         4.2       1
16     76         4.5       1
..
23     81         4.2       1
23     48         2.1       1
23     84         5.2       1
23     63         2.0       1