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Re: st: RE: AW: RE: Evaluating a set of conditions


From   Thomas Speidel <thomas@tmbx.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: AW: RE: Evaluating a set of conditions
Date   Wed, 23 Jun 2010 09:09:54 -0600

Thanks Martin and Nick. Here is an example where I have added more missing and manually created "disease" to clarify how the missing would impact the results:

    id   a   b   c   d   e   disease
     1   0   0   1   0   0         0
     2   1   0   1   1   0         1
     3   .   1   1   1   1         .
     4   0   1   1   0   1         0
     5   1   0   0   0   0         0
     6   1   .   1   1   0         1
     7   0   0   0   0   0         0
     8   1   .   .   .   1         .
     9   1   0   0   0   0         0
    10   1   .   .   1   1         1
    11   1   .   1   0   0         .
    12   1   0   1   0   0         0
    13   1   0   1   0   0         0
    14   .   0   1   0   0         .
    15   1   0   1   0   0         0
    16   1   0   1   1   0         1
    17   0   0   1   0   0         0
    18   1   .   .   0   .         .

Take a look at id==11 for example, where I don't have enough information to determine disease presence.

Thomas Speidel

Quoting Nick Cox <n.j.cox@durham.ac.uk> Wed 23 Jun 06:59:44 2010:

Yes, if there are missings it's more complicated than my initial answer
could suggest.

(a == 1) & (((b == 1) + (c ==1) + (d == 1) + (e == 1)) >= 2)

would seem to match the possibilities better.

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

Martin Weiss

The result does seem to differ much, though, from the one Thomas
evidently
wants - as expressed by his example:

*************
clear*
set obs 10000
set seed 12345

foreach var of newlist a b c d e{
	gen byte `var'=runiform()<.5
	replace `var'=. if runiform()<.15
}

//NJC
gen disease_true = a & (b + c + d + e >= 2) /*
*/  if !missing(a, b, c, d, e)

//Thomas
egen anytwo = rowtotal(a b c d e), missing
egen missing = rowmiss(a b c d e)
replace anytwo = . if (anytwo==0 & missing>=2 & missing<.)
replace anytwo = . if (anytwo==1 & missing==1)
replace anytwo = . if (anytwo==1 & missing==3)
replace anytwo = . if (missing>=4)
gen disease = 1 if (a==1 & anytwo>=2 & anytwo<.)
replace disease = 0 if (a==1 & anytwo<2)
replace disease = 0 if a==0
replace disease =. if a==.

//Comparison
compare disease_true disease
as  disease_true ==disease
*************

Nick Cox

I think you need to be clear whether missing means true, false or
indeterminate as far as this is concerned.

Setting aside missings, as a, b, c, d, e are Booleans (1 = true, 0 =
false) then

gen disease_true = a & (b + c + d + e >= 2)

is one way to do it. If missings make the problem indeterminate then
tack on

... if !missing(a, b, c, d, e)

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

Thomas Speidel

Following up on my previous post:
http://www.stata.com/statalist/archive/2010-06/msg00984.html
here is an example for something I am trying to achieve in a
nice/efficient/eleganty way.

I have a number of dummies: a, b, c, d, e (missing values do exist)
Disease=true if the following conditions are met:

1) a must be true AND
2) any two of b, c, d, e are true

As I said missing values are crucial, especially when evaluating the
second condition.

My current program works, but I don't think it is efficient and it
probably does things that are unnecessary:

*******************************************
egen anytwo = rowtotal(a b c d e), missing
egen missing = rowmiss(a b c d e)
replace anytwo = . if (anytwo==0 & missing>=2 & missing<.)
replace anytwo = . if (anytwo==1 & missing==1)
replace anytwo = . if (anytwo==1 & missing==3)
replace anytwo = . if (missing>=4)

gen disease = 1 if (a==1 & anytwo>=2 & anytwo<.)
replace disease = 0 if (a==1 & anytwo<2)
replace disease = 0 if a==0
replace disease =. if a==.
*******************************************

I tried to play around with cond, but I found it was making this much
more complicated then it is.  I know I am complicating my life more
than I need to which is why I am looking for alternative solutions.

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--
Thomas Speidel


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