Date: Tue, 7 Feb 2006 16:35:40 -0300
Reply-To: Hector Maletta <hmaletta@fibertel.com.ar>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Hector Maletta <hmaletta@fibertel.com.ar>
Subject: Re: Weight role in using MVA analysis
In-Reply-To: <LOEFKMFFPMGDNLEBHOFGIEFMCBAA.rclivio@tradelab.it>
Content-Type: text/plain; charset="us-ascii"
You write about weights "less than zero". I assume you mean "less than one".
Weights below zero make no sense, and are considered missing by SPSS. If you
actually have any negative weights, revise the way they were computed.
Weights cannot be negative, and also zero weights mean the case is excluded.
Now assuming the weights were not negative, please notice that MVA uses
regression for imputation, and for regression and other such procedures
weighting is essential to obtain unbiased results from disproportionate
samples. Increasing the scale of weights in a uniform manner (e.g.
multiplying all of them by 100) would affect the statistical significance
SPSS assigns to the results, since probability and standard errors in SPSS
are based on total WEIGHTED cases, but otherwise would yield the same
results as with your original weights. In your particular case I think
significance levels are not particularly important, but beware MVA would use
regression estimates it would otherwise consider non significant.
Hector
-----Mensaje original-----
De: Rita Clivio [mailto:rclivio@tradelab.it]
Enviado el: Tuesday, February 07, 2006 3:39 PM
Para: Hector Maletta; SPSSX-L@LISTSERV.UGA.EDU
Asunto: R: Weight role in using MVA analysis
Thanks Hector
I think you're right.
The number of cases that I have weighting the dabse is exactly the number of
cases with a weight less than zero.
And so ... do you think it's useful weighting the case before conducting
MVA?
If so could I use some trick (i.e. weigh * 100) in order to keep the
original proportionin dbase ?
Thanks again
Rita
-----Messaggio originale-----
Da: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]Per conto di
Hector Maletta
Inviato: martedi 7 febbraio 2006 19.15
A: SPSSX-L@LISTSERV.UGA.EDU
Oggetto: Re: Weight role in using MVA analysis
One possibility is that some of your weights (40%??) are zero or missing
values. Cases with zero or missing weights are not "seen" as cases by SPSS.
Zero weights may arise from non-zero fractional weights being rounded down
to zero.
Hector
-----Mensaje original-----
De: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] En nombre de Rita
Clivio
Enviado el: Tuesday, February 07, 2006 2:56 PM
Para: SPSSX-L@LISTSERV.UGA.EDU
Asunto: Weight role in using MVA analysis
Hi
I have a question for any kind soul ... :-)
Why if I conduct MVA on a weighted Database I find that I have replaced only
the 60% of the cases (i.e. I have a new file with replaced values that is
60% of all cases) ?
If I dont' weight, conducting MVA I have a new file with all values of the
dbase.
Weight is assigned to all cases in dbase.
Have you any idea ?
Thank in advance for your help ... and time .
Rita
