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# Re: st: Change of reference group in linear multiple regression analysis

 From Richard Williams To statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu Subject Re: st: Change of reference group in linear multiple regression analysis Date Thu, 09 Aug 2012 10:39:12 -0500

```At 08:38 AM 8/9/2012, Nick Cox wrote:
```
```Why not -recode- to say 1, 4, 8, 15, 25, 40 and use the quantitative
information you have? Sure, there is some arbitrariness involved, but
it is defensible.
```
```
```
I've done this myself. But does anybody know of any literature that defends (or attacks) the practice? It seems like the most difficult part is the open-ended upper category -- how should you choose a value for that?
```
```
```Nick

On Thu, Aug 9, 2012 at 2:30 PM, Richard Goldstein
<richgold@ix.netcom.com> wrote:

> I assume you are using an up-to-date version of Stata; see -h fvvarlist-
> and look under "base level"

On 8/9/12 9:25 AM, Amal Khanolkar wrote:

```
>> Hi, I'm currently running a linear multiple regression analysis where the principle explanatory variable is:
```>>
>> Years since |
>> immigration |      Freq.     Percent        Cum.
>> ------------+-----------------------------------
>>      <3 yrs |    106,794        3.57        3.57
>>     3-5 yrs |     91,311        3.05        6.62
>>    6-10 yrs |     96,657        3.23        9.85
>>   11-19 yrs |     82,344        2.75       12.61
>>   20-29 yrs |     50,954        1.70       14.31
>>    >=30 yrs |  2,563,396       85.69      100.00
>> ------------+-----------------------------------
>>       Total |  2,991,456      100.00
>>
```
>> - Currently the default group is the first category, <3yrs. I would however like to change this in the regression to the last group >=30 years. How do I do this without having to recode the above variable?
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```
```
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Richard Williams, Notre Dame Dept of Sociology
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```