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GAP Toolkit 5 Training in basic drug abuse data management and analysis Training session 7 SPSS: Recode and Compute

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Objectives To introduce and demonstrate SPSS tools for recoding variables and creating new variables To introduce and demonstrate the use of SPSS command syntax To introduce and demonstrate Help features in SPSS from a dialogue box

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Types of recode A categorical variable into a new set of categories A continuous variable into a categorical variable

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Recode approaches Into pre-defined categories of interest Into categories of equal size

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Example: pre-defined categories Recode weekly expenditure on drugs into the following categories: –Low expenditure <= £100 a week –High expenditure >= £101 a week

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select variable for recoding and click

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click here to map old new values

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FrequencyPercentValid percent Cumulative percent ValidLow3162.0 High1938.0 100.0 Total50100.0 Weekly drug expenditure

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Example: quantiles Recode weekly expenditure into the following: –4 categories, each with approximately the same number of cases (quartiles) –10 categories, each with approximately the same number of cases (deciles)

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FrequencyPercentValid percentCumulative percent Valid<=£901224.0 £91 <= X <= £981224.0 48.0 £99 <= X <= £1051326.0 74.0 £106 = £1161326.0 100.0 Total50100.0 NTILES of Expend

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FrequencyPercentageValid percentageCumulative percentage Valid1510.0 248.0 18.0 3714.0 32.0 448.0 40.0 548.0 48.0 6612.0 60.0 7510.0 70.0 8510.0 80.0 9612.0 92.0 1048.0 100.0 Total50100.0 NTILES of EXPEND

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Compute Creates new variables using: –Standard mathematical operators –A full range of functions –Conditional statements

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Transform/Compute click here to define variable type

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Type and Label

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Yexpend=Expend*52

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Explore: Yexpend StatisticStd. error Yearly drug expenditureMean5062.7277.468 95% Confidence Interval for Mean Lower Bound4907.04 Upper Bound5218.40 5% Trimmed Mean5072.89 Median5148.00 Variance300062.3 Std. Deviation547.779 Minimum3848 Maximum6032 Range2184 Interquartile Range754.00 Skewness-.333.337 Kurtosis-.446.662 Descriptives

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Example 2: Age Convert date of birth to age in years

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(DATE.DMY(01,01,2002) - dob) / (365.25*24*60*60)

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Explore: Age StatisticStd. error AGEMean25.431.219 95% Confidence Interval for Mean Lower Bound22.97 Upper Bound27.88 5% Trimmed Mean25.21 Median22.84 Variance72.867 Std. Deviation8.536 Minimum11 Maximum44 Range32 Interquartile Range12.77 Skewness.579.340 Kurtosis-.518.668 Descriptives

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Help Context-sensitive Help: –Right click on any part of a dialogue box to obtain help Dialogue box Help button

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Command language Command-line rather than Windows interface More flexible Reusable Saved as text files

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Syntax window Enter SPSS commands: –Type directly –Paste from a dialogue box Run SPSS commands Save as a text file

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The Paste button click to copy command into Syntax Window

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The Run menu

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Syntax for Age

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Summary Recode: –Into same variable –Into different variable Compute: –Mathematical operators –Functions Dialogue box Help: –Context-sensitive Help –Dialogue box Help button Command language: –Syntax Window –Dialogue box Paste button

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