Q1. How many possible values of Pearson r are there?

A1. Two, one negative and one positive.

Q2. How do you choose which one to use if no additional info is provided?

A2. I have no idea what you're fishing for here, Mike, but here's one

possible approach: Report the positive square root of r^2 and describe it

as the correlation between y and y-hat (which is always non-negative, even

if the correlation between x and y is negative).

Okay, now maybe you can tell us what you're really looking for! ;-)

Mike wrote

> This is a somewhat old chestnut, so let me provide a novel conundrum.

>

> Consider:

> A person reports the result of a correlational analysis and only reports

> the valuw od r^2. There are no scaterplots, no raw data, nthing except

> the "effect size" measure r^2.

>

> Question: What is the value of the Pearson r?

>

> A better question is "how values of Pearson r are there and how do you

> choose which one to use if no additional info is provided?" ;-)

>

> -Mike Palij

> New York University

> mp26@

>

> P.S. I'm getting well again.

>

>

> On Tue, Dec 11, 2018 at 11:54 AM Martin Holt <

> 000002126fbb7baa-dmarc-request@.uga

>> wrote:

>

>> *Xmas draws nearer!*

>>

>>

>> *For young statisticians...some festive fun*

>> *Proof that 2 = 1*

>> a = b

>> a2 = a.b

>> a2 + a2 = a.b + a2

>> 2a2 = a.b + a2

>> 2a2 – 2ab = a.b + a2 – 2ab

>> 2a2 – 2ab = a2 – a.b

>> 2(a2 – a.b) = a2 – a.b

>> Dividing through by (a2 – a.b) gives 2=1

>> Q.E.D.

>>

>> Martin P. Holt

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