PSY 216
Assignment 1 Answers
1. Problem 2 from the text
Define the terms parameter and statistic. Be sure that the concepts of population and sample are
included in your definition.
A parameter is a value, usually a number, which describes a population. A statistic is a value, usually a
number, which describes a sample.
2. Problem 3 from the text
Statistical methods are classified into two major categories: descriptive and inferential. Describe the
general purpose for the statistical methods in each category.
Descriptive statistics are used to describe the data. Typical descriptive statistics include measures of
central tendency (mean, median and mode) which describe the typical or average value of the data
and measures of dispersion (range, interquartile range, standard deviation, variance) which describe
the variability of the data (how different the observations are from each other). Inferential statistics
are used to help decide if a hypothesis is likely false. The help us decide if a treatment is effective or
whether two (or more) variables are related to each other.
3. Problem 15 from the text
In an experiment examining the effects of humor on memory, Schmidt (1994) showed participants a
list of sentences, half of which were humorous and half were non-humorous. The participants
consistently recalled more of the humorous sentences than the non-humorous sentences.
a. Identify the independent variable for this study.
The independent variable is the variable that the researcher manipulated. The variable that the
researcher manipulated is whether a sentence was humorous or not.
b. What scale of measurement is used for the independent variable?
The levels of the independent variable (non-humorous vs. humorous) are categories in no
particular order. Categories in no particular order are nominally scaled.
c. Identify the dependent variable for this study.
The dependent variable is the variable that the researcher measures. The variable that the
research measured is the number of sentences recalled.
d. What scale of measurement is used for the dependent variable?
The dependent variable has equally sized intervals – each sentence that is recalled increases the
dependent variable by the same amount. The zero point is absolute – if a person gets a score of 0
then they did not recall any of the sentences. When the intervals are equally sized and the 0 point
is absolute, it is a ratio scale.
4. Problem 18 from the text
For the following scores, find the value of each expression: (Problem 18 from the text)
X
4
2
1
5
a. ΣX = 4 + 2 + 1 + 5 = 12
b. ΣX2 = 42 + 22 + 12 + 52 = 16 + 4 + 1 + 25 = 46
c. (ΣX)2 = (4 + 2 + 1 + 5)2 = 122 = 144
d. Σ(X - 1) = (4 – 1) + (2 – 1) + (1 – 1) + (5 – 1) = 3 + 1 + 0 + 4 = 8
5. Problem 21 from the text
Two scores, X and Y, are recorded for each of n = 4 subjects. For these scores, find the value of each
expression
Subject
A
B
C
D
X
6
0
3
2
Y
4
10
8
3
X·Y
6x4=24
0x10=0
3x8=24
2x3=6
a. ΣX = 6 + 0 + 3 + 2 = 11
b. ΣX = 4 + 10 + 8 + 3 = 25
c. ΣXY = (6x4) + (0x10) + (3x8) + (2x3) = 24 + 0 + 24 + 6 =
54