Re: st: reshaping a data file: cell frequency = number of rows in the new data set

[Tom Trikalinos <ttrikalin@mac.com>]

Hi Gerben:
You would have to use _reshape long_ repeatedly and then _expand_.
As far as I get it, you have data on n studies in the following format

study TP FP FN TN
1      1  2  3  4
2     14 33 52 10
...
n      A  B  C  D

where the variables represent the 4 cells of the diagnostic table 
(TP=true positive, FP=false positive, FN=false negative, TN=true 
negative)
You could _reshape long_ in 2 steps:

First step: each study will occupy 2 lines, one for the positive and 
one for the negative counts per gold standard:
. ren TP posTest1
. ren FP posTest0
. ren FN negTest1
. ren TN negTest0
reshape long posTest negTest, i(study) j(goldStandardIs)

Second step: The same strategy. Each line (--> gold standard status per 
study) breaks in 2 lines, yielding 4 lines per study. First you have to 
uniquely identify the lines
. egen lineID = group(study goldStandardIs)
. ren posTest counts1
. ren negTest counts0
reshape long counts , i(lineID) j(testIs)

Now, each cell of the table is in a separate line. Coding is based on 
the dummies 'testIS' and 'goldStandardIs', as per your request; the 
variable 'counts' has each cell's counts.

Third step: expand the dataset and drop useless variables
expand counts
drop lineID counts

Hope this helps

tom



On Dec 17, 2004, at 2:12 AM, G. ter Riet wrote:


> Dear List members,
> In the context of a diagnostic meta-analysis, I have data from 2x2
> tables (cells a thru' d, signifying true positives, false positives,
> etc). My file has a wide format and is perfectly suited for a meta-
> analytic command like <metan a b c d, or>.
> As a hypothetical example, suppose one of my studies (rows) contained
> the cell frequencies 1 2 3 4, for variables a, b, c, d, respectively.
> How could I efficiently create another file (long format), based on
> these data, that looked like
> 1 1
> 1 0
> 1 0
> 0 1
> 0 1
> 0 1
> 0 0
> 0 0
> 0 0
> 0 0
> where the 1st column signified a binary test result, and the 2nd
> column a binary outcome according to a reference standard (gold
> standard test).
> Any help would be much appreciated.
>
> Gerben ter Riet, Amsterdam
>
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