|Date: ||Thu, 9 Nov 2000 13:35:56 +0000|
|Reply-To: ||Jeremy Miles <j.n.v.miles@DERBY.AC.UK>|
|Sender: ||"SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>|
|From: ||Jeremy Miles <j.n.v.miles@DERBY.AC.UK>|
|Subject: ||Re: simple regression reasoning|
|Content-Type: ||text/plain; charset="us-ascii"; format=flowed|
At 13:14 09/11/00, Jeff Mather wrote:
>I have a dependent variable (total events) and two IV's (total nurses,
>I have computed 2 ratio's, nurse's per bed (mean 0.4) or beds per nurse
>(mean 2.6). WHen I run a simple linear regression looking at about 50
>different hospitals, the R2 for beds per nurse regressed against events is
>significant, but the reverse ratio (nurses per bed) is not.
>What is the easiest way to explain why one is significant and the other is
It might be because you have transformed the data, thus changing the
Think of it as similar to rate and speed. Rate is hours per mile, speed is
miles per hour.
You do two things when you convert: 1) you change the shape of the
distribution, and 2) you change the linearity. Graph below shows the
conversion x axis is rate, y-axis is speed.
I would suggest that you have a good look at your residual plots and see if
anything is happening w.r.t. outliers, distributions or linearity.
Dr Jeremy Miles
Phone: 01332 592090, Fax: 01332 593131, Mobile: 07941 228018
Inst. of Behavioural Sciences, Derby University, Derby, DE22 3HL, UK
http://ibs.derby.ac.uk/~jeremym / http://www.jeremymiles.co.uk