Subtract variables when other variable condition is met

[Samia Aleem]

Hi everyone,
I'm fairly new at using stata and am having trouble figuring out the code for something.
I have a variable called AnxietyTScore. The score is measured at different points denoted by the variable Assmnt (1, 2 or 3). I need to calculate the difference in scores at Assmnt 1 and 2. The study has defined a meaningful change as a change of 5 in either direction. I then need to tabulate how many scores remained same, increased or decreased.
This is what the data looks like:

input float(Assmnt AnxietyTScore)
1 61.3
2 61.1
3 60.7
1 49.9
2 49.9
3 46.5
1 54.6
2 48.8
3 50.7
1 56.6
2 55.6
3 56.5
1 58.7
1 43.9
2 54.7
3 75.8
1 67.8
2 55.1
3 48.3
1 65.5
2 56.4
3 57.5
1 54
2 51.1
3 51.3
1 67.7
2 62.5
3 55.9
1 59.4
1 66.7
2 60.4
3 59.6
1 58.5
2 55.5
1 37.1
2 37.1
3 37.1
1 63.3
2 43.5
3 43.8
1 37.1
2 54.8
3 46.6
1 37.1
2 37.1
1 51.2
2 51.5
3 48.3
1 48.8
2 47.9
3 57
1 48.7
2 52
3 69.8
1 54.6
2 48.5
3 37.1
1 62.4
2 63.3
3 37.1
1 37.1
2 37.1
3 45.9
1 61.2
2 66.2
3 64.7
1 59.2
2 54.2
3 43.5
1 58.7
2 48.3
3 51
1 43.7
2 37.1
3 37.1
1 69
2 71.9
1 61.6
1 43.7
1 53.7
2 63.4
3 57.5
1 60.9
2 56.8
3 54.4
1 58.6
2 53.2
3 46.1
1 64.4
2 51.3
3 43.5
1 37.1
3 37.1
1 37.1
2 37.1
3 57.1
1 79.4
2 76.4
1 61.4
2 54
end
[/CODE]

Thank you!

[Rich Goldstein]

your write-up is not completely clear but I think this is what you request:

* calculate difference
gen wanted= AnxietyTScore-AnxietyTScore[_n-1] if Ass==2 & Ass[_n-1]==1

* categorize difference
gen byte wanted2=0 if abs(wanted)<5
replace wanted2=1 if wanted<=-5
replace wanted2=2 if wanted>=5 & wanted<.

*label the categories
la def wanted2 0 "same" 1 "decrease" 2 "increase"
la val wanted2 wanted2

you should change the variable names to ones that you want

[Nick Cox]

You surely and sorely need an identifier if you don't have one already. That's the first step. Here that's problematic. I've assumed that everyone has taken Assessment 1 which may be optimistic as there seem to be cases where Ass't 2 or Ass't 3 has been missed.

clear

input float(Assmnt AnxietyTScore)
1 61.3
2 61.1
3 60.7
1 49.9
2 49.9
3 46.5
1 54.6
2 48.8
3 50.7
1 56.6
2 55.6
3 56.5
1 58.7
1 43.9
2 54.7
3 75.8
1 67.8
2 55.1
3 48.3
1 65.5
2 56.4
3 57.5
1 54
2 51.1
3 51.3
1 67.7
2 62.5
3 55.9
1 59.4
1 66.7
2 60.4
3 59.6
1 58.5
2 55.5
1 37.1
2 37.1
3 37.1
1 63.3
2 43.5
3 43.8
1 37.1
2 54.8
3 46.6
1 37.1
2 37.1
1 51.2
2 51.5
3 48.3
1 48.8
2 47.9
3 57
1 48.7
2 52
3 69.8
1 54.6
2 48.5
3 37.1
1 62.4
2 63.3
3 37.1
1 37.1
2 37.1
3 45.9
1 61.2
2 66.2
3 64.7
1 59.2
2 54.2
3 43.5
1 58.7
2 48.3
3 51
1 43.7
2 37.1
3 37.1
1 69
2 71.9
1 61.6
1 43.7
1 53.7
2 63.4
3 57.5
1 60.9
2 56.8
3 54.4
1 58.6
2 53.2
3 46.1
1 64.4
2 51.3
3 43.5
1 37.1
3 37.1
1 37.1
2 37.1
3 57.1
1 79.4
2 76.4
1 61.4
2 54
end

gen id = sum(Assmnt == 1)

bysort id (Assmnt) : gen difference = Anxiety[2] - Anxiety[1] if Assmnt[1] == 1 & Assmnt[2] == 2
format difference %2.1f

gen change = cond(abs(difference) > 5, sign(difference), 0)

tabdisp id, c(difference change)

egen tag = tag(id)

tab change if tag

. tabdisp id, c(difference change)

----------------------------------
       id | difference      change
----------+-----------------------
        1 |       -0.2           0
        2 |        0.0           0
        3 |       -5.8          -1
        4 |       -1.0           0
        5 |                      
        6 |       10.8           1
        7 |      -12.7          -1
        8 |       -9.1          -1
        9 |       -2.9           0
       10 |       -5.2          -1
       11 |                      
       12 |       -6.3          -1
       13 |       -3.0           0
       14 |        0.0           0
       15 |      -19.8          -1
       16 |       17.7           1
       17 |        0.0           0
       18 |        0.3           0
       19 |       -0.9           0
       20 |        3.3           0
       21 |       -6.1          -1
       22 |        0.9           0
       23 |        0.0           0
       24 |        5.0           0
       25 |       -5.0           0
       26 |      -10.4          -1
       27 |       -6.6          -1
       28 |        2.9           0
       29 |                      
       30 |                      
       31 |        9.7           1
       32 |       -4.1           0
       33 |       -5.4          -1
       34 |      -13.1          -1
       35 |                      
       36 |        0.0           0
       37 |       -3.0           0
       38 |       -7.4          -1
----------------------------------

.
. egen tag = tag(id)

.
. tab change if tag

     change |      Freq.     Percent        Cum.
------------+-----------------------------------
         -1 |         12       36.36       36.36
          0 |         18       54.55       90.91
          1 |          3        9.09      100.00
------------+-----------------------------------
      Total |         33      100.00