st: loops

[Arun Rajamohan <arajamoh@uwo.ca>]

Hi,

I am dealing with huge datasets for which I have to estimate  
percentile exposure time within two to three subsets. I noticed  
something that happened there and tried duplicating it with a stata  
example dataset [webuse beetle] and I noticed it again. Attached  
below is the do file modified for beetle dataset.

/* Stata/IC 10.0 for Macintosh */
/* Do file to assess LD10-90 for beetle.dta */
/* Obtain beetle from webuse beetle */
use ~/desktop/beetle.dta
gen p=r/n
forvalues i=1/3 {
glm p ldose if beetle==`i', f(b)
	forvalues j=0.1(0.1)0.9 {
	local k=`j'*100
	display as text "LD `k' = " as result (log(`j'/(1-`j'))-_b[_cons])/_b 
[ldose]
	}
}

A part of the result for beetle.dta looks like this...


Generalized linear models                          No. of obs       
=         8
Optimization     : ML                              Residual df      
=         6
                                                   Scale parameter  
=         1
Deviance         =  .4046285206                    (1/df) Deviance  
=  .0674381
Pearson          =  .3998784961                    (1/df) Pearson   
=  .0666464

Variance function: V(u) = u*(1-u/1)                [Binomial]
Link function    : g(u) = ln(u/(1-u))              [Logit]

                                                   AIC              
=  1.029287
Log likelihood   = -2.117148142                    BIC             =  
-12.07202

------------------------------------------------------------------------ 
------
             |                 OIM
           p |      Coef.   Std. Err.      z    P>|z|     [95% Conf.  
Interval]
------------- 
+----------------------------------------------------------------
       ldose |   36.74959   24.12731     1.52   0.128     
-10.53907    84.03825
       _cons |  -65.29355   43.00475    -1.52   0.129     
-149.5813    18.99422
------------------------------------------------------------------------ 
------
LD 10 = 1.7169257
LD 20 = 1.7389921
LD 30 = 1.7536588
LD 40 = 1.7656816
LD 50 = 1.7767148
LD 60 = 1.787748
LD 70 = 1.7997708
LD 80 = 1.8144375
LD 89.99999999999999 = 1.8365039


Why is this last LD 90 showing as 89.99... ... . Am I doing something  
odd (bad math) in the do file?

Thanks,
A

Arun Rajamohan
Department of Biology
University of Western Ontario
London, Ontario N6A 5B7, CANADA.
519 661 2111 80582


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