The Psychopathy Checklist – Revised (PCL—R) is an assessment tool used to identify psychopaths, with scores ranging from 0 to 40 (a score of 30 or higher being indicative of psychopathy)
A forensic psychologist interested in the prevalence of psychopaths in a
prison administered the PCL—R to 74 random prison inmates and obtained the following
distribution of scores. Convert this into a grouped frequency distribution containing five
class intervals, and (a) determine the size of the class intervals, (b) indicate the upper and
lower limits of each class interval, (c) identify the midpoint of each class interval, (d) find
the percentage for each class interval, (e) find the cumulative frequency for each class
interval, and (f) find the cumulative percentage for each class interval.
Score Value f
39 4
38 4
35 2
32 3
31 4
27 9
26 7
25 6
21 13
20 10
17 5
15 7
N = 74
What would be an ideal response?
Score Value f
35-39 10
30-34 7
25-29 22
20-24 23
15-19 12
N = 74
a.
39.5 34.5
5
i U L = ?
= ?
=
b. 34.5-39.5, 29.5-34.5, 24.5-29.5,19.5-24.5,14.5-19.5
c. m : 37,32,27,22,17
d.
( )
( )
( )
( )
Percentage for class interval 35 39 10 / 74 * 100 13.5%
Percentage for class interval 30-34 7 / 74 * 100 9.5%
Percentage for class interval 25-29 22 / 74 * 100 29.7%
Percentage for class interval 20-24 23 / 74 * 100
? = =
= =
= =
= =
( )
31.1%
Percentage for class interval 15-19 12 / 74 * 100 16.2% = =
e. cf: 74, 64, 57, 35, 12
f. 100.0, 86.5, 77, 47.3, 16.2
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