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st: RE: Re: RE: RE: RE: RE: RE: RE: Dependent variable [with zero mass point]


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Re: RE: RE: RE: RE: RE: RE: Dependent variable [with zero mass point]
Date   Wed, 6 Sep 2006 16:45:15 +0100

Many of the zeros could thus be by-products 
of the researchers or even the companies using 
the same figure as before, and/or of a practice
of reporting figures in rounded form. Thus at 
least some very likely "should be" small positives or 
small negatives. 

In land use studies a certain country was widely 
praised for holding its forest cover constant while
all around it were visibly losing cover year by 
year. It turned out that in the absence of an
annual survey the people who should know were 
just returning the last measurement available
in response to a request for the current figure. 
Came a new survey, and an apparent enormous drop
in one year, and a post mortem on what on earth 
had happened....

However, it could also be that zero here signals
poor data quality for certain companies, something
that might be checkable in other ways. 

Nick 
n.j.cox@durham.ac.uk 

Francesca Gagliardi
 
> Thank you very much for your replies to my question. I 
> apologise for not 
> having specified better how my dependent variable has been 
> obtained. It is 
> just a growth rate of firms, calculated as (employees at time 
> t - employees 
> at time t-1)/employees at time t-1. I have 15678 
> observations, of which 
> 23.7%  are negative values, 39.2% are zeros and the remaining 
> are positive values
> 

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