BST 322
Week 4 Assignment
1.
For each correlation coefficient below, calculate what proportion of variance is shared by
the two correlated variables:
a.
r
= 0.25

b.
r
= 0.33
r
= 0.90

c.
r

d.

2.
For each coefficient of determination below, calculate the value of the correlation
coefficient:
a.
r
2
r
2

b.

c.
r
2
r
2
= 0.07

d.

3.
Suppose a researcher regressed surgical patients’ length of stay (dependent variable) in
the hospital on a scale of functional ability measured 24 hours after surgery.
Given the
following, solve for the value of the intercept constant and write out the full regression
equation given:
Mean length of stay = 6.5days
( Y= outcome variable)
Mean score on the functional ability scale = 30
(x= actual value of variable x)
Slope of the regression equation = -0.10
(b= slope of the line (regression coefficient))
a.
Solve the equation
Y= a +bX

b. Write out the full regression equation
Y= 9.5 + (-0.10)(x)

4.
Now using the regression equation that was calculated in Exercise 3, compute the
predicted value of Y (the length of the hospital stay) for patients with the following
functional ability scores measured 24 hours after surgery:
a.
42

b.
68
25

c.

d.
10