----- Original Message -----
From: Andrew O'Connor DO <[email protected]>
Date: Thursday, April 26, 2007 8:09 am
Subject: Re: st: RE: Using Stata to calculate proportion of observation
time above a threshold value i.e. "ti
To: [email protected]
> Thanks for your help Scott,
> This is sort of what I was looking for, but rather than
> calculating the
> predicted values for missing data, I'm trying to use the available
> datato measure the proportion of each individuals observation time
> (eachperson has a variable number of observations and a variable
> total period
> (calendar days) of observation) that their blood pressures were
> above a
> set threshold.
> Put another way, if time is on the X axis, Systolic BP on the Y
> axis, I
> can easily draw a graph with connected BP's over time. Now if I
> draw a
> horizontal line at say 140 on the y axis, how do I calculate the
> proportion of the total period of observation that blood pressures
are
> above the threshold value.
> Thanks again
> AO
>
How about this:
clear
input pt_id str9 appt_date str9 appt_status bp_systolic
1 "21 Apr 05" "No Show" .
1 "07 Jun 05" "Completed" 140
1 "11 Jan 06" "Completed" 150
1 "16 Feb 06" "Completed" 150
1 "30 Mar 06" "Canceled" .
1 "02 May 06" "Canceled" .
1 "09 May 06" "Completed" 138
1 "11 Jul 06" "Completed" 142
1 "19 Sep 06" "Completed" 150
2 "30 May 06" "No Show" .
2 "11 Jul 06" "Completed" 176
2 "25 Jul 06" "Completed" 121
2 "01 Aug 06" "Canceled" .
2 "01 Aug 06" "Completed" 101
2 "15 Aug 06" "Completed" 118
2 "22 Aug 06" "Canceled" .
2 "12 Sep 06" "Completed" 136
2 "14 Nov 06" "Completed" 137
2 "16 Jan 07" "Completed" 113
2 "06 Feb 07" "No Show" .
2 "03 May 06" "Canceled" .
2 "25 Jul 06" "Canceled" .
2 "01 Aug 06" "Canceled" .
2 "07 Feb 07" "Canceled" .
end
gen date = date(appt_d, "dm20y")
format date %d
sort pt date appt_s
by pt (date): drop if date == date[_n+1]
//Create a variable with the proportion above threshold
local threshold = 140
gen proportion=.
levelsof pt, local(levels)
foreach l of local levels {
count if pt == `l' & bp !=.
local total =r(N)
count if bp > `threshold' & bp !=. & pt == `l'
replace proportion = r(N)/`total' if pt == `l'
}
l, sepby(pt) ab(20)
//Creating a results dataset
tempname memhold
tempfile results
postfile `memhold' id proportion using `results'
foreach l of local levels {
count if pt == `l' & bp !=.
local total =r(N)
count if bp > `threshold' & bp !=. & pt == `l'
local proportion = r(N)/`total'
post `memhold' (`l') (`proportion')
}
postclose `memhold'
preserve
use `results',clear
l, ab(20)
restore
Scott
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
