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Correlation

So you want to correlate. SAS's Proc Corr is the way to goProc Corr data=Data1;Default is Pearson correlationProduces a correlation matrix of continuous variablesBut will try to correlate anything you tell it to.Provides descriptive statisticsDoes pairwise or listwise deletion. Pairwise

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Correlation

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    1. Jacob Seybert 10/22/09 Correlation!

    2. So you want to correlate… SAS’s Proc Corr is the way to go Proc Corr data=Data1; Default is Pearson correlation Produces a correlation matrix of continuous variables But will try to correlate anything you tell it to. Provides descriptive statistics Does pairwise or listwise deletion

    3. Pairwise vs. Listwise Deletion Listwise deletion - if any data is missing deletes entire case from analysis For listwise deletion use a NOMISS statement Proc Corr data=Data1 NOMISS; Pairwise deletion - uses the data it can, to correlate variables Default

    4. Proc Corr Syntax Default with no Var statement is to correlate all variables using Pearson Proc Corr data=Data1 <OPTIONS>; Var var1 var2 var3; By groupingvariable; *Data must have been sorted previously; Run;

    5. <Options>! No brackets < > Can have more than one! Options: NOMISS - Exclude observations with missing analysis values from the analysis PEARSON - Request Pearson product-moment correlation SPEARMAN - Request Spearman rank-order correlation FISHER PEARSON - Request Pearson correlation statistics using Fisher's z transformation FISHER SPEARMAN - Request Spearman rank-order correlation statistics using Fisher’s z transformation ALPHA - Compute Cronbach's coefficient alpha

    6. Example “CorrExample.sas” No statements:

    7. No Statement Results

    8. Example Continued With a By statement

    9. By Statement Results

    10. Example Continued Testing for correlation for specific variables

    11. 3 Variable Results

    12. Other Run Combinations Separately by gender for 3 variables With listwise deletion And more…

    13. More <Options>! No brackets < > Same location as noted previously Options: BEST= - Display a specified number of correlation coefficients NOCORR - Suppress Pearson correlations NOPRINT - Suppress all printed output NOPROB - Suppress p-values NOSIMPLE - Suppress descriptive statistics RANK - Displays the ordered correlation coefficients for each variable, from highest to lowest.

    14. Options Example Listwise deletion Rank With SPEARMAN correlations Calculating coefficient apha

    15. Outputs Output Results

    16. Creating Scatterplots of Data Proc GPLOT data=Data1; plot SelfEst*SupportParnt; Symbol1 Value = x INTERPOL = rl; Run; Value = the symbol to use to represent the datapoint Interpol= if you want to draw a line between points based on the left, right or center of the data. rl command tells it to create a new point to the right and left of each statement

    17. Symbols Used to Plot

    18. Example:

    19. Or… Use Excel! Have to delete missing values yourself Steps: Highlight the two columns of data to plot Click “Insert” Click “Scatter” arrow Add a trend line

    20. Scatterplot in Excel

    21. Add a Trend Line

    22. Brannick’s Excel Correlation Spreadsheet Provides a variety of useful correlation coefficent tests. Will help with homework Lets play with it!

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