data analysis: frequencies gap toolkit 5 training in basic drug abuse data management and analysis...
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Data analysis: frequencies
GAP Toolkit 5 Training in basic drug abuse data management and analysis
Training session 8
Objectives
• Introduce univariate, descriptive statistics as the first step in a process of data analysis, starting from exploration and moving towards more sophisticated techniques
• Distinguish between frequencies and relative frequencies
• Introduce frequency and probability distributions as data models
Descriptive Statistics
• Univariate• Categorical data• Continuous data
SPSS Descriptive Statistics
• Analyse/Descriptive Statistics/Frequencies• Analyse/Descriptive Statistics/Explore• Analyse/Descriptive Statistics/Descriptives
Frequency vs relative frequency
• “The frequency of any value of a variable is the number of times that value occurs in the data; that is, a frequency is a count. The relative frequency of any value is the proportion or fraction or percent of all observations that have that value.”
(D. S. Moore, Statistics: Concepts and Controversies, 5th ed. (New York, W. H. Freeman Press, 2000)).
Frequency distribution/probability distribution
• Frequency distribution: all possible values of the variable and their associated counts
• Probability distribution: all possible values of the variable and their associated probabilities (relative frequencies)
Percentages
• Let: – f1 = the number of cases in category 1– n = the total number of cases
• The percentage of cases in category 1:
%100*1 n
f
Exercise: frequency of referral
• Construct a frequency table for referral source in the file main.sav
Frequency Percent Valid Percent Cumulative Percent
Valid Self/Fam/Friends 586 37.3 38.0 38.0
Employer 195 12.4 12.7 50.7
Health Pro 194 12.3 12.6 63.3
Religious Grp 65 4.1 4.2 67.5
Hosp/Clinic 53 3.4 3.4 70.9
Welfare 252 16.0 16.4 87.3
Courts/Corrections 100 6.4 6.5 93.8
School 64 4.1 4.2 97.9
Unknown 32 2.0 2.1 100.0
Total 1541 98.1 100.0
Missing System 30 1.9
Total 1571 100.0
Referral
Frequencies: Format button
Frequency Percent Valid Percent Cumulative Percent
Valid Self/fam/friends 586 37.3 38.0 38.0
Welfare 252 16.0 16.4 54.4
Employer 195 12.4 12.7 67.0
Health pro 194 12.3 12.6 79.6
Courts/corrections 100 6.4 6.5 86.1
Religious grp 65 4.1 4.2 90.3
School 64 4.1 4.2 94.5
Hosp/clinic 53 3.4 3.4 97.9
Unknown 32 2.0 2.1 100.0
Total 1541 98.1 100.0
Missing System 30 1.9
Total 1571 100.0
Referral
Frequencies: Charts button
Referral
Referral
Unknown
Hosp/Clinic
School
Relgious Grp
Courts/Corrections
Health Pro
Employer
Welfare
Self/Fam/Friends
Pe
rce
nt
50
40
30
20
10
0
Frequencies: Statistics button
Referral
N Valid 1541
Missing 30
Mode 1
Statistics
Frequencies: syntax
• FREQUENCIES• VARIABLES=refsourc• /FORMAT=DFREQ• /STATISTICS=MODE• /BARCHART PERCENT• /ORDER=ANALYSIS.
Exercise: frequencies
• Generate a frequency table and bar chart for each of the following variables and comment:– Race– Education– Employment
• Save the output and the syntax file
Frequency: Race
Frequency Percent Valid Percent Cumulative Percent
Valid Coloured 722 46.0 52.8 52.8
White 520 33.1 38.0 90.8
African 109 6.9 8.0 98.8
Asian 17 1.1 1.2 100.0
Total 1368 87.1 100.0
Missing System 203 12.9
Total 1571 100.0
Race
Frequency: Education
Frequency Percent Valid Percent Cumulative Percent
Valid Secondary 978 62.3 64.3 64.3
Primary 332 21.1 21.8 86.2
Tertiary 189 12.0 12.4 98.6
None/pre-primary 21 1.3 1.4 100.0
Total 1520 96.8 100.0
Missing System 51 3.2
Total 1571 100.0
Education
Frequency: Employment
Frequency Percent Valid Percent Cumulative Percent
Valid Working full-time 571 36.3 36.6 36.6
Not working 569 36.2 36.4 73.0
Student/pupil 240 15.3 15.4 88.3
Working part-time 68 4.3 4.4 92.7
Pensioner 34 2.2 2.2 94.9
Disabled 33 2.1 2.1 97.0
Housewife 28 1.8 1.8 98.8
Other 18 1.1 1.2 99.9
Apprentice 1 .1 .1 100.0
Total 1562 99.4 100.0
Missing System 9 .6
Total 1571 100.0
Employment
Summary
• Frequencies and relative frequencies• Frequency distributions and probability distributions• Format/ordering• Bar charts• Statistics/mode