Analyses using SPSS version 19 Chiara Haller, Harvard University

Introduction to SPSS (Andy Field) Objectives Knowledge: How to use statistical analyses logically How to create/structure a dataset How to clean up the dataset How to create frequency tables Descriptive statistics: Graphs (box-plot, dispersion diagrams) Stratify the analysis Literature: Introduction to SPSS (Andy Field)

Data acquisition Name Date of Birth Weight/height Sex Type it directly into SPSS? Into Excel and - Import the data - Copy the data into SPSS Whatever you decide, keep a back up of your original dataset!!

Missing data Input a value which must not be confused with any other value. For example giving it a coding which does not exist in the rest of the data (i.e., -99). Attention: Don’t forget to tell SPSS that these are missings! means without correct coding

The Compute function Calculate scores on behalf of existing variables Example: Calculate BMI on behalf of the variables weight and height

Commande RECODE Recode Variables Example: Recode height into 3 categories

The syntax It’s possible to keep all the analyses in a file Instead of OK, press PASTE, and your commands are being opened as syntax, which can now be saved. There are 3 windows you work with on SPSS: Dataset: Variable view, data view Output Syntax Each of these windows can be saved.

Descriptive statistics Mean Variance / standard deviation Minimum / Maximum … (click options for more)

Box-plot ¼ Extreme Values Upper quartile (3rd quartile) Mediane ¼ (top 25%) ¼ Extreme Values Mediane Lower quartile (1st quartile Upper quartile (3rd quartile) «interquartile range» ¼ (bottom 25%) Minimal Value

Scatter Plot

Stratify the analysis It is often useful to split a sample in several sub-samples Three possibilities: Split the file Select the preferred observations Perform the analysis by stratifying the variable

Split files Exercise: Re-analyze the descriptive statistics

Select the preferred observations Exercise: Re-analyze the descriptive statistics

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