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

[Thomas Speidel <thomas@tmbx.com>]

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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