Correlation coefficient with repeated measures

Posted by Margaret MacDougall on Feb 21, 2007; 11:18am
URL: http://spssx-discussion.165.s1.nabble.com/Correlation-coefficient-with-repeated-measures-tp1073970.html

Hello

  I am considering work that has already been carried out in relation to the comparison of continuous measurements obtained using two procedures. For each procedure, there is more than one rater but the raters are not necessarily identical across the two procedures. Suppose the sample variances for the two procedures are denoted by 'sampvar1' and 'sampvar2', respectively and that the covariance between the measurements under procedures 1 and 2 is denoted by Cov(X_1, X_2). The formula
  Cov(X_1, X_2)/sqrt(sampvar1*sampvar2) appears to be an analogue of the Pearson Product Moment Correlation Coefficient (in which there are no repeated measures).

  However, I am having some difficulty understanding how this formula works in practice with repeated measures. In particular:

  1) can the coefficient be calculated using SPSS when there are repeated measures and if so can you please provide some assistance?

  2) can you provide a reference to explain the underlying mathematics?

  One main conceptual difficulty I am experiencing here is that of understanding which values would be matched with one another in determining the covariance between measurements from procedure 1 and procedure 2 when it is already known that the raters in both methods are not identical. This problem carries over, of course to the interpretation of the correlation coefficient itself.

  I look forward very much to having some light shed on these issues.

  Many thanks

  Best wishes

  Margaret



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