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st: Re: Making Cohorts

From   ajjee <>
Subject   st: Re: Making Cohorts
Date   Thu, 28 Oct 2010 04:14:52 -0700 (PDT)


I want to implement the following strategy on my data.

Consider now the basic linear individual effect model

yit = ai + bXit + uit    i = 1,…N; t = 1,…T       eq(1)

where Xit is a (K x 1) vector of explanatory variables which we assume
exogenous to the model, index t and
i refer to time and individuals respectively.
Assuming, for simplicity, that there is a unique regressor (K = 1), if we
aggregate all observations to cohort level, the resulting model can be
written as

(y-bar)_ct = (a-bar)_ct + b(x-bar)_ct + (u-bar)_ct                c = 1,…C

where (x-bar)_ct is the average value of all observed xit’s in cohort c at
time t, and analogously for the other variables in the model. The resulting
data set is a pseudo panel with repeated observations over T periods and C

now I want to make cohorts (say for) birth year and then want to aggregate
the data as above.  But I have 15 countries also and I want to analyse
particular attitudes in countries based on three year surveys(6 waves).

Thanks and Regards,


Maarten buis wrote:
> --- On Thu, 28/10/10, ajjee <> wrote:
>> But I am still confused about COHORT. When I create this by
>> cohort=year-age, now it gives me year of birth of each
>> respondent. Now I want to group each respondent in a unique
>> cohort.  I'm quoting procedure from a paper
>> "Define C cohorts, which are groups of individuals sharing
>> some common characteristic like sex or date of birth. These
>> groups are defined in such a manner that each individual is
>> a member of exactly one cohort, and remains a member of this
>> cohort for all periods. For example, a particular cohort may
>> consist of all male individuals born in 1945–1949."
> So, year of birth is one form of cohort: it defines groups that
> are born in a given year.  The fact that this confuses you is 
> an example of common mistake: Just because something has its 
> own name does not mean that it is special or difficult.  A 
> cohort, as you defined it, is just another name for a variable 
> that you want to treat as categorical.
> If you want another categorization, then you need to tell us
> exactly what you want. As the definition you quoted above says
> there are an extremely large number of ways in which you can 
> group observations.
> Hope this helps,
> Maarten
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
> --------------------------
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