[EMAIL PROTECTED] wrote: > > The fact that the shorter scale has low internal consistency doesn't necessarily > mean that the 4 items in question are not unidimensional. It may just be that > the measurement error is large relative to their covariance. Given that the > four items in question are drawn from a scale with established internal > consistency, I'd suspect they probably are measuring the same thing - only not > measuring it very well. > > purnima. > No, there is a flaw in the logic here. If a scale has "established internal consistency" (usually based on a high Cronbach alpha value), a researcher CANNOT conclude that the items are "measuring the same thing". All it takes for alpha to be high is that each item correlates well with at least some other items, but not necessarily with all of them. Alpha is a good indicator of the relative freedom of the items in a scale from random measurement error. It is NOT a sound indicator of unidimensionality. The misconception that it is such an indicator is widespread. Paul Gardner
begin:vcard n:Gardner;Dr Paul tel;cell:0412 275 623 tel;fax:Int + 61 3 9905 2779 (Faculty office) tel;home:Int + 61 3 9578 4724 tel;work:Int + 61 3 9905 2854 x-mozilla-html:FALSE adr:;;;;;; version:2.1 email;internet:[EMAIL PROTECTED] x-mozilla-cpt:;27600 fn:Dr Paul Gardner, Reader in Education and Director, Research Degrees, Faculty of Education, Monash University, Clayton, Vic. Australia 3800 end:vcard
