[Rasch] interpreting principal components of analysis

Julie Johnson aruba_2006 at yahoo.com
Thu Feb 9 04:33:49 EST 2006

  Date: Mon, 6 Feb 2006 15:37:42 -0800 (PST)
From: Julie Johnson <aruba_2006 at yahoo.com>
Subject: interpreting principal components of analysis
To: rasch at acer.edu.au

  I am a beginning Rasch user and am having difficulty interpreting the principal components of analysis print outs.  I am hoping that my results are positive and would appreciate some assistance for experienced Rasch users.
  My results from Table 23.2 are below.
         Contrast 1 extracts 3.5 units out of 56 units of Item residual variance noise.
         Yardstick (variance explained by measures)-to-This Contrast ratio: 25.1:1
         Yardstick-to-Total Noise ratio (total variance of residuals): 1.6:1
  Table of STANDARDIZED RESIDUAL variance (in Eigenvalue units)
                                                  Empirical       Modeled
  Total variance in observations     =        143.6 100.0%         100.0%
  Variance explained by measures     =         87.6  61.0%          61.1%
  Unexplained variance (total)       =         56.0  39.0% 100.0%   38.9%
  Unexplned variance in 1st contrast =          3.5   2.4%   6.2%
  Thanks for your input,
  Julie Johnson

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