Okun
PSY 230
STUDY GUIDE #1
I. Course Overview.
II. Rationale for Studying Statistics
1.
Why study statistics?
III. Definition of Basic Terms
2.
How can we distinguish between (a) a population and a sample; (b) a parameter and a
statistic, (c) descriptive and inferential statistics, and (d) a variable and a constant?
3.
What are the different types of variables? Why is it important to take into account the
type of variable?
IV. Summation Notation
4.
Why is summation notation important? How does it work?
What is the difference between (a) (X)2 and X2; and (b) X Y and XY?
PARTICIPANT #
X
Y
5
4
3
2
1
ACT
20
29
26
32
23
SAT
400
550
500
600
450
The (X)2 operation involves summing the scores on the X variable before squaring them.
The X2 operation involves squaring the scores on the X variable before summing them.
The X Y operation involves summing the scores on the X variable and summing the scores
on the Y variable before multiply the sum of the X scores by the sum of
the Y scores.
The XY operation involves multiplying each person’s score on the X variable by his or her
corresponding score on the Y variable before summing the products.
Assuming all positive numbers, (X)2 > X2 and X Y > XY
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V.
Frequency Distributions
5.
What is a frequency distribution?
A distribution refers to how a set of scores are dispersed.
Frequency refers to how often each score occurs. A frequency
distribution for a quantitative variable orders the scores from
low to high and tells us how many people got each score.
6.
Given a set of observations, how can an ungrouped
frequency distribution be created?
A simple (ungrouped)frequency
variable shows the frequency,
score. The symbol for simple
individual f’s for each score
distribution for a quantitative
or number of people, who got each
frequency is f. The sum of the
equals N, the sample size.
FIRST TEST SCORES in PSY 230: Spring 2006 (N = 50)
96
88
91
88
91
79
92
98
82
93
92
77
84
95
98
86
93
93
94
96
88
95
84
86
100
81
87
84
88
91
89
96
98
99
93
2
89
89
79
89
81
94
86
76
93
90
85
86
88
98
60
Scores
Tallies
Frequencies
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64
63
62
61
60
/
/
////
1
1
4
0
3
2
2
5
2
3
1
4
5
1
4
1
3
0
1
2
0
2
0
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
///
//
//
/////
//
///
/
////
/////
/
////
/
///
/
//
//
/
/
/
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7.
Given a set of observations, how can a grouped frequency
distribution be created?
With a grouped frequency distribution, the raw scores on the
variable (X) are grouped into classes of scores. In a grouped
frequency distribution, the size or width of each class interval
will always be an integer and the minimum value of the integer
will always be 2.
GROUPED FREQUENCY DISTRIBUTION
FOR 50 FIRST TEST SCORES in PSY 230
Class Interval
Tallies
Frequency
100-103
96-99
92-95
88-91
84-87
80-83
76-79
72-75
68-71
64-67
60-63
/
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/
4
1
8
11
13
9
3
4
0
0
0
1
8. What is the main advantage and what is the main disadvantage of
using a grouped as opposed to an ungrouped frequency
distribution?
9. What are some common ways that the guidelines for frequency
distributions are violated?
10.
How can a frequency distribution be converted to a
cumulative frequency distribution?
FIRST TEST SCORES IN PSY 230 (N = 50)
X
f
cf
________________________
100-103
1
50
96-99
8
49
92-95
11
41
88-91
13
30
84-87
9
17
80-83
3
8
76-79
4
5
72-75
0
1
68-71
0
1
64-67
0
1
60-63
1
1
________________________
X = first test scores
f = frequency in each class interval
cf = cumulative frequency = the frequency of all scores at or below
the highest score in a class interval.
5