[Rasch] Fan

Anthony James luckyantonio2003 at yahoo.com
Mon Oct 29 20:37:55 EST 2007


Hi there,
  Fan (1998) argues that item and person statistics based on CTT and IRT are very similar and the complexities of IRT are not worthwhile.
  Has this been reacted to by the Rasch and IRT communities?
  I’d be thankful for any sources that are brought to my attention.
   
  Is replicating Fan’s research worthwhile?
   
  This is my own view:
  Item and person raw scores are the sufficient statistics in the Rasch model and item and person measures are based on these and highly correlate with raw scores. Therefore, one will always get Fan’s results. What fan hasn’t apparently noticed is the robustness of the person and item measures in the Rasch measurement to the idiocyncracies of the test and sample. 
  He’s arguing on the basis of high correlations (obtained from large and homogeneous groups) which simply mean the rank order of the items and persons remain the same regardless of the testing theory. This can hardly be news.
  S/he defines the high-ability group “as those whose scores fall within the 15th and 100th percentile ….low-ability group was defined as those whose scores fall within the 0 to 85th percentile range…” (p.363). Most of this sampling is shared. They have a lot in common. 
   
  Ben Wright’s 1968 experiment (Memo#1) provides the acid test for the comparison of the two models. 
  Cheers
  Anthony

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