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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/Friends Employer Health Pro Religious Grp Hosp/Clinic Welfare Courts/Corrections School Unknown Total MissingSystem301.9 Total Referral

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Frequencies: Format button

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FrequencyPercentValid PercentCumulative Percent ValidSelf/fam/friends Welfare Employer Health pro Courts/corrections Religious grp School Hosp/clinic Unknown Total MissingSystem301.9 Total 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 ValidColoured White African Asian Total MissingSystem Total Race

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Frequency: Education FrequencyPercentValid PercentCumulative Percent ValidSecondary Primary Tertiary None/pre-primary Total MissingSystem513.2 Total Education

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Frequency: Employment FrequencyPercentValid PercentCumulative Percent ValidWorking full-time Not working Student/pupil Working part-time Pensioner Disabled Housewife Other Apprentice Total MissingSystem9.6 Total 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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