The meaning of "contribute unique variance"

Question

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.}

Stephie · Accepted Answer · 2015-07-09 08:48:11Z

1

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.

answered Jul 9, 2015 at 8:48

Stephie

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Thank you, what is the role of unique? does it main the certain? or same for both of knowledge?
– Ahmad
Commented Jul 9, 2015 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
Commented Jul 9, 2015 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
Commented Jul 9, 2015 at 11:01

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