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Re: st: Recency Weighted cumulative exposures


From   "Carmine Rossi, Mr" <[email protected]>
To   "<[email protected]>" <[email protected]>
Subject   Re: st: Recency Weighted cumulative exposures
Date   Thu, 14 Nov 2013 00:42:28 +0000

Hi Mr. Radyakin,

Thank you very much for your email and help. However, the code is not correct.

There are two issues: 1) The number of observations per ID is not constant, so for the macro `mt', it would need to be specific per id. For example, ID==1 has 5 time points, and ID==2 has 4 time points.

2) The weights are not fixed. This is more difficult for me to explain, but I will try.

To get the "result" for ID==1 and time==5, I used the spreadsheet calculations shown in the previous email.
However, if I was to calculate the "result" at time==4, I would use the following weights:

id time  dose delta_t       w(t)      dose(t)*weight(t)        cumulative_sum
1     1      0        3               0.88              0                 0
1   2        0        2               0.94              0                 0
1  3        2.6      1                0.99               2.574        2.574
1  4       2.6       0                1                 2.6           5.174

Notice how, now the weight, w(t), at time==4 is equal to 1, when I want to calculate the cumulative sum at time==4.

For this reason, I thought I would need loops, and this is why I am asking the STATA community for help. My major issue is that the weight’s are not fixed and they change depending on the cumulative sum that I want to calculate at each time point.

Thank you again for trying to help,
-Carmine Rossi
PhD Candidate, Epidemiology
[email protected]

On 2013-11-13, at 5:23 PM, Sergiy Radyakin <[email protected]> wrote:

> Carmine, no loops are really necessary:
> 
> do http://radyakin.org/statalist/2013111301/recencyw.do
> 
> Hope this helps, Sergiy Radyakin
> 
> 
> On Wed, Nov 13, 2013 at 5:08 PM, Carmine Rossi, Mr
> <[email protected]> wrote:
>> Dear STATA listers,
>> 
>> I have the following repeated measures data on two subjects with a dose exposure variable. I am interested in creating a variable called “result” that is a recency-weighted cumulative sum.
>> 
>> id   time   dose         result
>> 1     1    0              0
>> 1     2    0              0
>> 1     3    2.6            2.6
>> 1     4    2.6            5.174
>> 1     5    3.2            8.218
>> 2     1    0              0
>> 2     2    0              0
>> 2     3    0.7            0.7
>> 2     4    0.7            1.393
>> 
>> The “result” variable is obtained as a cumulative sum using a weight function:
>> Summation of (Dose(i)  x weight(t)), where the weight function is:
>> 
>> W(t) = exp((-(delta time)2)/70.70)
>> 
>> So to get the weighted cumulative sum value of 8.218 (for subject 1 at time 5), rather than 8.4, which would have been the un-weighted cumulative sum, I did the following in a spreadsheet.
>> 
>> 
>> Id time     dose     delta_t       w(t)      dose(t)*weight(t)        cumulative_sum
>> 1   1        0         4           0.80                0                                             0
>> 1   2        0         3           0.88                0                                             0
>> 1   3       2.6        2           0.94              2.444                                 2.444
>> 1   4       2.6        1           0.99              2.574                                 5.018
>> 1   5       3.2        0            1                 3.2                                       8.218
>> 
>> Is there a way to do this in STATA with loops? Can anyone provide any suggestions?
>> 
>> 
>> Carmine Rossi
>> PhD Candidate, Epidemiology
>> McGill University
>> [email protected]
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