OkunPSY 230STUDY 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 #XY

ACTSAT

520400

429550

326500

232600

123450

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X2and X Y XY

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 ungroupedfrequency distribution be created?

A simple (ungrouped)frequency distribution for a quantitative variable shows the frequency, or number of people, who got each score. The symbol for simple frequency is f. The sum of the individual f’s for each score equals N, the sample size.

FIRST TEST SCORES in PSY 230: Spring 2006 (N = 50)

96799286888189899485

88927793958796898686

91988493848498797688

88829594868899899398

91939896 1009193819060

ScoresTalliesFrequencies

100/1

99/1

98////4

970

96///3

95//2

94//2

93/////5

92//2

91///3

90/1

89////4

88/////5

87/1

86////4

85/1

84///3

830

82/1

81//2

800

79//2

780

77/1

76/1

750

740

730

720

710

700

690

680

670

660

650

640

630

620

610

60/1

7. Given a set of observations, how can a groupedfrequency 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 / /
////////
///////////
/////////////
/////////
///
////
/ / 1
8
11
13
9
3
4
0
0
0
1

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)

Xfcf

______

100-103150

96-99849

92-95 1141

88-91 1330

84-87917

80-833 8

76-794 5

72-750 1

68-710 1

64-670 1

60-631 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.

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