Problem 7.15: Lunchtime.
a) The correlation between time toddlers spent at the table
and the number of calories consumed by the toddlers is r
b) If time spent at the table were recorded in hours
instead of minutes, the correlation would not change at
all. Correlation is calculated from z-scores, and since
these unitless measures of position are unaffected by
changes in scale, correlation is likewise unaffected.
c) The correlation between time spent at the table and
calorie consumption for toddlers is –0.649, a moderate,
negative correlation. Toddlers who spent more time at
the table tended to consume fewer calories.
d) The analyst’s remark is speculative. There are many
possible explanations for the behaviour of the toddlers.
The data merely show us an association between time
spent at the table and calories consumed by toddlers,
and association is not the same thing as a cause-and-
Problem7.33 Thrills. The scatterplot at the right shows that
the association between Drop and Duration is straight,
positive, and weak, with no outliers. Generally, rides on
coasters with a greater initial drop tend to last somewhat
longer. The correlation between Drop and Duration is 0.35,
indicating a weak association. Problem 8.1: Regression equations.
x sx y
a) 10 2 20
b) 2 0.06 7.2 1.2
c) 12 6 152 30
d) 2.5 1.2 25 100
b1= y y = 0 + 1 x
y = b0+ b1x
(0.5)(3) 20= b + 0.75(10)
b1= 2 0
y = b + b x
y = 0 + 1 x