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Data analysis: frequencies GAP Toolkit 5 Training in basic drug abuse data management and analysis Training session 8

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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

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Descriptive Statistics Univariate Categorical data Continuous data

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SPSS Descriptive Statistics Analyse/Descriptive Statistics/Frequencies Analyse/Descriptive Statistics/Explore Analyse/Descriptive Statistics/Descriptives

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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)).

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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)

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Percentages Let: –f 1 = the number of cases in category 1 –n = the total number of cases The percentage of cases in category 1:

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Exercise: frequency of referral Construct a frequency table for referral source in the file main.sav

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FrequencyPercentValid PercentCumulative Percent ValidSelf/Fam/Friends58637.338.0 Employer19512.412.750.7 Health Pro19412.312.663.3 Religious Grp654.14.267.5 Hosp/Clinic533.4 70.9 Welfare25216.016.487.3 Courts/Corrections1006.46.593.8 School644.14.297.9 Unknown322.02.1100.0 Total154198.1100.0 MissingSystem301.9 Total1571100.0 Referral

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Frequencies: Format button

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FrequencyPercentValid PercentCumulative Percent ValidSelf/fam/friends58637.338.0 Welfare25216.016.454.4 Employer19512.412.767.0 Health pro19412.312.679.6 Courts/corrections1006.46.586.1 Religious grp654.14.290.3 School644.14.294.5 Hosp/clinic533.4 97.9 Unknown322.02.1100.0 Total154198.1100.0 MissingSystem301.9 Total1571100.0 Referral

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Frequencies: Charts button

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Frequencies: Statistics button

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Referral NValid1541 Missing30 Mode1 Statistics

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Frequencies: syntax FREQUENCIES VARIABLES=refsourc /FORMAT=DFREQ /STATISTICS=MODE /BARCHART PERCENT /ORDER=ANALYSIS.

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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

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Frequency: Race FrequencyPercentValid PercentCumulative Percent ValidColoured72246.052.8 White52033.138.090.8 African1096.98.098.8 Asian171.11.2100.0 Total136887.1100.0 MissingSystem20312.9 Total1571100.0 Race

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Frequency: Education FrequencyPercentValid PercentCumulative Percent ValidSecondary97862.364.3 Primary33221.121.886.2 Tertiary18912.012.498.6 None/pre-primary211.31.4100.0 Total152096.8100.0 MissingSystem513.2 Total1571100.0 Education

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Frequency: Employment FrequencyPercentValid PercentCumulative Percent ValidWorking full-time57136.336.6 Not working56936.236.473.0 Student/pupil24015.315.488.3 Working part-time684.34.492.7 Pensioner342.2 94.9 Disabled332.1 97.0 Housewife281.8 98.8 Other181.11.299.9 Apprentice1.1 100.0 Total156299.4100.0 MissingSystem9.6 Total1571100.0 Employment

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Summary Frequencies and relative frequencies Frequency distributions and probability distributions Format/ordering Bar charts Statistics/mode

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