What is the usage and meaning of "contribute unique variance" in this sentence?

For children with typical language, orthographic knowledge and morphological knowledge contributed unique variance to spelling performance.

Source: Werfel, K.L., & Schuele, C.M. (2012, November).
Contribution of linguistic knowledge to spelling performance in elementary school children with and without language impairment. Poster presented at the Annual Convention of the American Speech-Language-Hearing Association, Atlanta, GA.


We are talking about statistics here.

Variance gives the way / to which degree the meassured data (in this case: spelling performance) is distributed.

Contribute here means play a part in, influence something.

So in plain English (non-mathematician translation w/o having read the paper),

Orthographic knowledge and morphological knowledge both influence the meassurable variance of the spelling performance in a characteristic way.

  • Thank you, what is the role of unique? does it main the certain? or same for both of knowledge? – Ahmad Jul 9 '15 at 10:10
  • It's "unique variance", but I can only guess at what it means exactly - I would assume each type of knowledge having a different influence. – Stephie Jul 9 '15 at 10:22
  • I didn't study it completely, but I think two knowledge (orthography and morphological) are in the same category and have the same effect. I am even suspicious that he means "Orthographic and morphological knowledge contribute unique variance to spelling performance." – Ahmad Jul 9 '15 at 11:01

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