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From |
Jeph Herrin <junk@spandrel.net> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: RE: coding problem: looping through a list of ID's |

Date |
Mon, 24 Nov 2008 13:40:48 -0500 |

I'm sure this is a very interesting problem, but it is hard to see quite what you want or where you are starting. You say you reshaped the data twice, which may have helped you or may have distorted your observations. Assuming your original data looks like this: ID dov height 1 1 . . 2 2 . and what you want is average annual increase, then bysort ID (dov) : gen rate=(height-height[_n-1])/(dov-dov[_n-1]) bysort ID: egen average=mean(rate) The first line will give you the rate of increase/day for each subject at each visit relative to the last (note that -rate- will be missing for the first visit). The second line then averages this rate over all visits. Note that the rate will be in height/day, you will want to multiply by 365.25 to get growth/year. Hope this helps. Jeph Leny Mathew wrote:

Figured as much, but at this point any comments would be useful for me!! When I got this data set each patient had a different number of visits over the period of time and not everyone visits over whole period. I tried writing this code for that but couldn't get it to loop over patient id, so had to create a max(number of visits) per person and use that value as a break point. The I changed the data into wide format and when I reshaped it back to long, I ended up with the everybody having the maximum of 148 visits. This was a boon in a sense because I didn't have to worry about the max number of visits per person (a problem as each loop takes an awful lot of time!) Some people would have age as missing in some rows but I figured that it wouldn't be a problem in the loop as that difference would be set to missing and that wouldn't be an issue. Since I needed to create an age interval I thought that age could be used in the same way as I would use date, just that I would set 1 year instead of the number of days elapsed. The way this is set up I'm trying to take the difference (within each patient) of age[i]- age[j] where i takes all values 148 through 1 and j does the same. So I can calculate the all age differences and if the age difference is between approximately 1 year ( 0.95, 1.5) then I can calculate the height difference for those ages. The data is as follows: pt_id counter num timec age dov 1 1 148 1 10.1 1 jan 01 1 2 148 2 12.1 1 jan 03 . . 1 147 148 147 . . 1 148 148 148 16.1 .. 2 149 148 1 5.0 2 Jan 98 2 150 148 2 5.5 2 Jun 98 . . . **************************************************************************************************************** On Mon, Nov 24, 2008 at 10:34 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:I don't know how you propose to withdraw this if anyone objects. For the record, I can't see any violation of protocol here, just a question that looks unlikely to get much of an answer. You may be lucky, but few people want to wade through code as convoluted as this, especially when you advertise in advance that it is wrong. I note that despite your statement that "not everybody has 148 measurements" you are jumping by 148 in your code. That sounds like a recipe for problems. I note also that you are not using dates in your calculations, but counters. I suggest you start again and show us the structure of the data and define more precisely how height increase over a year is to be defined from measurements irregular in time. Nick n.j.cox@durham.ac.uk Leny Mathew I've have been using stata for a while but am a novice when it comes to loops and macros. I'm hoping that someone on the list could help with with the following problem. I have a data set with 74 patients each with 148 measurements of height over a period of 10 years. The height measurements for all cases are not necessarily at the same time and not everybody has 148 measurements. The number 148 is a result of changing the data set into the long form. I'm trying to calculate the the the increase in height for a one year (approximately) interval for each case. I developed the following code for this purpose, but am not able to get it to work perfectly. It loops though each patient, but at the end, 'phv' end up being the same for everyone in the data. Also, this code might be a totally convoluted way of doing this and I'm hoping that someone could give me some pointers on how to improve/ revamp this completely. If this posting is a violation of the list protocol on type of posting, please feel free to let me know and I'll take it off. I've spent quite some time tweaking this and am out of ideas. I'm using stata10.1 Any suggestions are much appreciated. Note: 'dov' is date of visit, used to create age. sort pt_id dov by pt_id: gen timec=_n gen counter=_n sort pt_id dov by pt_id: gen num=_N local j=counter local i=1 local k=1 while pt_id <75 { display pt_id[_n] while (pt_id[`j']==pt_id[`j'+1]) & timec < 148{ local value= max(`j'+147, num[pt_id]) while (`value' > max(`j',1)) & (`value' > timec[`j']) & (pt_id[`j']==`k') { replace phv= (pt_ht[`value']-pt_ht[counter[`i']]) if ((age[`value']-age[counter[`i']]) >0.95 & (age[`value']-age[counter[`i']]) < 1.5) & (pt_id[`j']==`k') local i= `i'+1 if `i'==`value' local value= `value'-1 if `i'==`value'+1 & pt_id[`j']==1 local i=1 if `i'==`value'+1 & (pt_id[`j'] >1) local i=(`k'-1)*148 } local i=`i'+148 local j=`j'+148 display `j' local k=`k'+1 display `k' continue if k >74 break } } **I tried to use phv[`value'] so that it would replace the value at the certain row, but that gave me an error that weights are not allowed. (I'm sure that that must have been a violation of stata rules!) * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/* * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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**Follow-Ups**:**Re: st: RE: coding problem: looping through a list of ID's***From:*"Leny Mathew" <lenymathewc@gmail.com>

**References**:**st: coding problem: looping through a list of ID's***From:*"Leny Mathew" <lenymathewc@gmail.com>

**st: RE: coding problem: looping through a list of ID's***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**Re: st: RE: coding problem: looping through a list of ID's***From:*"Leny Mathew" <lenymathewc@gmail.com>

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