chapter 2 organizing the data
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Chapter 2 Organizing the Data. Frequency Distributions of Nominal Data. Formulas and statistical techniques used by social researchers to: Organize raw data Test hypotheses Raw data is often difficult to synthesize Most common types of distributions are: Frequency Percentage Combination. - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 2Organizing the Data
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Frequency Distributions of Nominal Data
• Formulas and statistical techniques used by social researchers to:• Organize raw data• Test hypotheses
• Raw data is often difficult to synthesize• Most common types of distributions are:
• Frequency• Percentage• Combination
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Nominal Data and Distributions
Responses of Young Boys to Removal of Toy
Response of Child f
Cry 25
Express Anger 15
Withdraw 5
Ply with another toy 5
N=50
Frequency distribution of nominal data consists of two columns:
• Left column has characteristics (e.g., Response of Child)
• Right column has frequency (f)
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Comparing Distributions• Comparisons clarify and add information
Response to Removal of Toy by Gender of Child
Gender of Child
Response of Child Male Female
Cry 25 14
Express Anger 15 1
Withdraw 5 2
Play with another toy 5 8
Total 50 25
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Proportions and Percentages• Proportions - Compares the
number of cases in a given category with the total size of the distribution
• Most prefer percentages to show relative size.
• Percentage – The frequency per 100 cases
N
fP
Formula for proportion
N
f100%
Formula for percentage
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Illustration: Gender of Students Majoring in CJ(f)
Criminal Justice Majors
Gender College A College B
Male 879 119
Female 473 64
Total 1,352 183
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Illustration: Gender of Students Majoring in CJ (f and
%)Criminal Justice Majors
College A College B
Gender
f % f %
Male 879 65 119 65
Female
473 35 64 35
Total 1,352 100 183 100
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Rates
• Rates usually preferred by social researchers
• Rate – comparison between actual and potential cases
• Base terms in rates may vary
casespotentialf
casesactualfRate 000,1
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Rate of Change• Compare the same
population at two points in time
• Rate of Change =
time 2f – time1f
time 1f(100)*
Year Theft Rate1
% Change
2005 120.3
2006 127.4 5.9%
2007 116.8 -8.3%
2008 107.4 -8.0%
2009 98.7 -8.1%
2010 94.6 -4.2%
1Source: National Crime Victimization Survey
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Ordinal/Interval Data and Distributions
Attitudes Toward Televised Trials
F
Slightly Favorable 9
Somewhat Unfavorable 7
Strongly Favorable 10
Slightly Unfavorable 6
Strongly Unfavorable 12
Somewhat Favorable 21
Total 65
Incorrect
Attitudes Toward Televised Trials
F
Strongly Favorable 10
Somewhat Favorable 21
Slightly Favorable 9
Slightly Unfavorable 6
Somewhat Unfavorable 7
Strongly Unfavorable 12
Total 65
Correct
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Frequency Distribution of Final-Examination Grades for 71 Students
Grade f Grade f Grade f Grade f
99 0 85 2 71 4 57 0
98 1 84 1 70 9 56 1
97 0 83 0 69 3 55 0
96 1 82 3 68 5 54 1
95 1 81 1 67 1 53 0
94 0 80 2 66 3 52 1
93 0 79 8 65 0 51 1
92 1 78 1 64 1 50 1
91 1 77 0 63 2 N = 71
90 0 76 2 62 0
89 1 75 1 61 0
88 0 74 1 60 2
87 1 73 1 59 3
86 0 72 2 58 1
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Grouped Frequency Distributions of Interval DataGrouped Frequency Distribution of Final-Examination Grades for 71 Students
Class Interval f %
95-99 3 4.23
90-94 2 2.82
85-89 4 5.63
80-84 7 9.86
75-79 12 16.90
70-74 17 23.94
65-69 12 16.90
60-64 5 7.04
55-59 5 7.04
50-54 4 5.63
71 100
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Flexible Class IntervalsIncome Category F %
$100,000 and above 16,886 21.9
$75,000-$99,999 10,471 13.5
$50,000-$74,000 15,754 20.3
$40,000-$49,999 7488 9.7
$30,000-$39,999 7996 10.3
$20,000-$29,999 8169 10.6
$15,000-$19,999 3709 4.8
$10,000-$14,999 2890 3.7
$5000-$9999 2024 2.6
Under $5000 2031 2.6
N = 77688
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Cumulative Distributions• Cumulative frequencies involve the total number of
cases having a given score or a score that is lower• Cumulative frequency shown as cf• cf obtained by the sum of frequencies in that
category plus all lower category frequencies• Cumulative percentage – percentage of cases having
any score or a lower score
N
cfc )100(%
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Grouped Frequency Distributions of Interval DataGrouped Frequency Distribution of Final-Examination Grades for 71 Students
Class Interval f %
95-99 3 4.23
90-94 2 2.82
85-89 4 5.63
80-84 7 9.86
75-79 12 16.90
70-74 17 23.94
65-69 12 16.90
60-64 5 7.04
55-59 5 7.04
50-54 4 5.63
71 100
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Grouped Frequency Distributions of Interval DataGrouped Frequency Distribution of Final-Examination Grades for 71 Students
Class Interval f Cf % C%
95-99 3 71 4.23 100
90-94 2 68 2.82 95.76
85-89 4 66 5.63 92.94
80-84 7 62 9.86 87.31
75-79 12 55 16.90 77.45
70-74 17 43 23.94 60.55
65-69 12 26 16.90 36.31
60-64 5 14 7.04 19.71
55-59 5 9 7.04 12.67
50-54 4 4 5.63 5.63
71 100
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Frequency Distribution of Seat Belt Use
Use of Seat Belts f %
All the time 499 50.1
Most of the time 176 17.7
Some of the time 124 12.4
Seldom 83 8.3
Never 115 11.5
Total 997 100
Cross-tabCross-Tabulation of Seat Belt Use by Gender
Gender of Respondents
Use of Seat Belts Male Female Total
All the time 144 355 499
Most of the time 66 110 176
Some of the time 58 66 124
Seldom 39 44 83
Never 60 55 115
Total 367 630 997
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What Type to Choose?• There are three sets of percentages
• Total • Row • Column
• All are correct, mathematically speaking • Total percentages may be misleading • Row and column percentages come down to which is more
relevant to the purpose of the analysis
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Cross-tab Formulas
totalN
ftotal )100(%
rowN
frow )100(%
Formula for total percents columnN
fcol )100(%
Formula for row percents
Formula for column percents
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Cross Tabulations – Victim-Offender Relationship by Gender of Victim for
Homicides in US for 2005 (With Row%)Victim-Offender Relationship
Gender Intimate Intimate % Family Family % Other Other % Total Total %
Male 617 1,310 11,235 13,161
Female 1,470 639 1,421 3,531
Total 2,087 1,949 12,656 16,692
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Cross Tabulations – Victim-Offender Relationship by Gender of Victim for
Homicides in US for 2005 (With Row%)Victim-Offender Relationship
Gender Intimate Intimate % Family Family % Other Other % Total Total %
Male 617 4.7% 1,310 10.0% 11,235 85.4% 13,161 100%
Female 1,470 41.6% 639 18.1% 1,421 40.2% 3,531 100%
Total 2,087 12.5% 1,949 11.7% 12,656 75.8% 16,692 100%
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Cross Tabulations –Victim-Offender Relationship by Gender of Victim for
Homicides in US for 2005 (With Column%)
Victim-Offender Relationship
Male Female Total
Intimate 617 1,470 2,087
Family 1,310 639 1,949
Acquaintance 7,237 998 8,235
Stranger 3,998 423 4,421
Total 13,161 3,531 16,692
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Cross Tabulations –Victim-Offender Relationship by Gender of Victim for
Homicides in US for 2005 (With Column%)
Victim-Offender Relationship
Male Female Total
Intimate 617 1,470 2,087
4.7% 41.6% 12.5%
Family 1,310 639 1,949
10.0% 18.1% 11.7%
Acquaintance 7,237 998 8,235
55.0% 28.3% 49.3%
Stranger 3,998 423 4,421
30.4% 12.0% 26.5%
Total 13,161 3,531 16,692
100% 100% 100%
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Graphic Presentations
• Graphs are useful tools to emphasize certain aspects of data.
• Many prefer graphs to tables.• Types of graphs include:
• Pie charts, bar graphs, frequency polygons, line charts, and maps
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Single22.6%
Married61.2%
Widowed7.3%
Divorced8.9%
Pie Chart of Marital StatusSource: Bureau of the Census
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Exploded Pie ChartFigure 2.3 Pie Chart of Marital Status
Source: Bureau of the Census
Divorced8.9%
Widowed7.3%
Single22.6%
Married61.2%
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Bar GraphBar Graph of Seat Belt Use (with percents)
0
10
20
30
40
50
60
Never Seldom Sometimes Most times All times
Seat belt use
Per
cen
t
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Histogram of Distribution of Children in Little Rock Community Survey
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Frequency Polygon for Distribution of Student Examination Grades
0
5
10
15
20
52 57 62 67 72 77 82 87 92 97
Midpoint
Fre
quen
cyFrequency Polygon Example
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Janu
ary
Febr
uary
Mar
chAp
rilMay
June Ju
ly
Augu
st
Sept
embe
r
Octob
er
Novem
ber
Decem
ber
0
2000
4000
6000
8000
10000
12000
14000
MarijuannaAlcoholHallucinogens
Number of Adolescents (< 18 y/o) Using for the First Time by Month
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Shape of a Distribution
• Kurtosis • Leptokurtic • Platykurtic • Mesokurtic
• Skewness• Negative • Positive
• Normal Curve
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Kurtosis
Leptokurtic Platykurtic Mesokurtic
Some Variation in Kurtosis among Symmetrical Distributions
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Skewness
Negatively skewed Positively skewed Symmetrical(Normal)
Three Distributions Representing Direction of Skewness
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Summary• Organizing raw data is critical• Data can be summarized using frequency
distributions.• Comparisons of groups possible through
proportions, percentages and rates.• Cross-tabs allow dimensional (and more) analysis• Graphic presentations:
• help to emphasize findings • make data more accessible to consumers of research• help researchers identify trends