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Questions about correlations

  1. How should I deal with outliers when doing correlations?

  2. Rank-based and other correlations (percentage bend) which are robust to non-Normal data

  3. How do I correlate change in score with the score at baseline?

  4. How do I measure agreement to see if two measures are measuring the same thing (Bland and Altman plots)?

  5. Can I do a correlation between two variables where one variable is less than or equal to the other?

  6. How do I produce nonparametric Spearman partial correlations using SPSS?

  7. What is Collinearity in multiple regression, and what do I do about it?

  8. How do I compare a pair of correlations?

  9. How do I obtain an average correlation?

  10. How do I work out reliability for three or more items? (Cronbach's alpha, composite reliability and Raykov's rho)

  11. What thresholds should I use for convergent validity?

  12. How do I test if a correlation is zero and obtain its confidence interval?

  13. How many degrees of freedom are associated with a test of whether a zero-order or multiple correlation equals zero?

  14. How do I estimate a pooled correlation using multiple scores from a set of subjects?

  15. How do I adjust p-values to test if more than one correlation is zero?

  16. How do I obtain a 95% confidence interval for a correlation (or slope in a simple regression) in SPSS?

  17. How do I adjust a correlation for group differences (using partial and semi-partial correlations)?

  18. Power calculations for testing if correlations equal zero

  19. What are polychoric correlations and how do I compute them and use in SPSS?

  20. What are intraclass correlations and how do I use them?

  21. How do I compute consistency across subjects using an intraclass correlation?

  22. A note on correcting for restriction of ranges which underestimate Pearson correlations

  23. What is the relationship between significance tests of regression coefficients and of correlation coefficients?