Re: Pooled data and Logistic Regression

Posted by Art Kendall on Apr 04, 2011; 1:28pm
URL: http://spssx-discussion.165.s1.nabble.com/Pooled-data-and-Logistic-Regression-tp4279890p4281762.html

Once I saw two actual occasions when dichotomizing variables was useful.

Back when logistic regression was new a presenter wanted to describe what logistic regression was. She did not have a data set with a dichotomous DV so she used an existing data set. [This was late 70's, before the web, so it was not easy to find an appropriate data set quickly.]  Unfortunately, the audience did not grasp immediately that she was just doing a demo of LR itself, and lambasted her for "committing a nefarious median split". That ate up a lot of the time for her presentation.

On another occasion a presenter wanted to demonstrate the futility of the median split. 

Have you experienced any occasion where it made sense to dichotomize?

Art

On 4/4/2011 9:05 AM, Bruce Weaver wrote:

Dare I ask why you want to dichotomize?  More often than not, it's a bad
idea:  You throw away information and lose power.  There are several good
articles on the topic, including this very readable one by Dave Streiner.

  https://ww1.cpa-apc.org/publications/archives/cjp/2002/april/streiner.PDF

HTH.



jaya609 wrote:

Dear Listserv,

I used Multiple Imputation in SPSS 17 MVA.
Now, I want to dichotomize my DVs based on their median value.
However, in frequencies output, I did not see median for POOLED dataset.
How can I get it?

The next step is Logistic Regression.
Some tables of Logistic Regression output.... I did not get the result of
pooled dataset.
Those tables are...
Omnibus tests of model coefficients, Model summary, and Classification
table.
Is there any way to get the results of pooled dataset on these tables?
If it's not.... how can I report my results?

JHK

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