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Re: st: age: factor variables may not contain noninteger values


From   Lars Folkestad <lfolkestad@health.sdu.dk>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: age: factor variables may not contain noninteger values
Date   Tue, 8 Nov 2011 20:47:37 +0100

Thats true but biologically when i'm 39years and 10 months i'm closer to
40 than 39. 
Im not sure it makes a difference but it might - floor may potentially
underestimate the effect of age.

lars

Den 08/11/11 20.39 skrev "Nick Cox" <njcoxstata@gmail.com>:

>All that said, as age as an integer usually means "age last birthday",
>I am surprised that -round()- is regarded as the answer. I would put
>my foot down for -floor()-.
>
>For example, I am 19 and will not be 20 until next birthday.
>
>Nick
>
>On Tue, Nov 8, 2011 at 7:29 PM, Lars Folkestad <lfolkestad@health.sdu.dk>
>wrote:
>> Thank you for that jesper. It sure did the trick.
>> lars
>>
>> Den 08/11/11 13.17 skrev "Jesper Lindhardsen" <JESLIN01@geh.regionh.dk>:
>>
>>>Hi Lars,
>>>
>>>Try
>>>
>>>
>>>g new_age= round(age_var,1)
>>>
>>>
>>>HTH,
>>>
>>>Jesper
>>>
>>>-----Original Message-----
>>>From: owner-statalist@hsphsun2.harvard.edu
>>>[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Lars
>>>Folkestad
>>>Sent: 08 November 2011 12:14
>>>To: statalist@hsphsun2.harvard.edu
>>>Subject: Re: st: age: factor variables may not contain noninteger values
>>>
>>>This helps a lot.
>>>Thank you.
>>>
>>>But i have a question about the second point.
>>>Is there a quick and easy way to round the age to the nearest integer
>>>value? I could use the floor / ceil functions, but some of the ages
>>>Should be rounded up and some should be rounded down.
>>>
>>>lars
>>>
>>>Den 08/11/11 11.40 skrev "Maarten Buis" <maartenlbuis@gmail.com>:
>>>
>>>>On Tue, Nov 8, 2011 at 11:13 AM, Lars Folkestad wrote:
>>>>> I am trying to investigate the interactions between age and a
>>>grouping
>>>>>variable in a regression model, using this code:
>>>>>
>>>>> xi: regress Var1 age##i.group
>>>>>
>>>>> Var1: is a continuous variable
>>>>> Age: is a continous variable / float
>>>>>
>>>>> When i run the code i get the following error message:
>>>>> age:  factor variables may not contain noninteger values
>>>>
>>>>First, you are mixing -xi- and factor variable notation. You should
>>>>just leave the -xi:- prefix away.
>>>>
>>>>Second, in most surveys I am aware of age will be measured in whole
>>>>years. In those cases age should only contain integer values and this
>>>>error message means I made an error while preparing the data. This is
>>>>true regardless of how the data is stored. However, this is not
>>>>necessarily an error, you could have fractional age if you had for
>>>>instance exact birth dates and exact dates at which events of interest
>>>>happen. Alternatively, I may have standardized age or rescaled it so
>>>>it is measured in decades rather than years. However, in the latter
>>>>two cases I would have created new with different variable names
>>>>(probably z_age and age_d). So I would check whether non-integer age
>>>>would make sense given the way your data was collected.
>>>>
>>>>Third, whether there is an error or not you probably want -regress
>>>>var1 c.age##i.group- i.e. tread age as a continuous variable and not
>>>>as a set of dummies.
>>>>
>>>>Hope this helps,
>>>>Maarten
>>>>
>>>>--------------------------
>>>>Maarten L. Buis
>>>>Institut fuer Soziologie
>>>>Universitaet Tuebingen
>>>>Wilhelmstrasse 36
>>>>72074 Tuebingen
>>>>Germany
>>>>
>>>>
>>>>http://www.maartenbuis.nl
>>>>--------------------------
>>>>
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