Dear All,
I have individual level panel data that includes spells, with a 6 month *follow up* period after each spell as follows:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input double(id month) byte spell float spell_followup double(base_y followup_y) float followupmonth
52   1 0 .                 .                  . .
52   2 0 .                 .                  . .
52   3 0 .                 .                  . .
52   4 0 .                 .                  . .
52   5 0 .                 .                  . .
52   6 0 .                 .                  . .
52   7 0 .                 .                  . .
52   8 0 .                 .                  . .
52   9 0 .                 .                  . .
52  10 0 .                 .                  . .
52  11 0 .                 .                  . .
52  12 0 .                 .                  . .
52  13 0 .                 .                  . .
52  14 0 .                 .                  . .
52  15 0 .                 .                  . .
52  16 0 .                 .                  . .
52  17 1 .                 .                  . .
52  18 1 .                 .                  . .
52  19 1 .                 .                  . .
52  20 1 . 30.35714340209961                  . .
52  21 0 1                 .              21.25 1
52  22 2 1                 .              21.25 2
52  23 2 1                 .              21.25 3
52  24 2 1                 .              21.25 4
52  25 2 1                 .              21.25 5
52  26 2 1             21.25              21.25 6
52  27 0 2                 .                  0 1
52  28 0 2                 .  32.04545593261719 2
52  29 0 2                 .  69.54545593261719 3
52  30 0 2                 .                 75 4
52  31 0 2                 .               37.5 5
52  32 0 2                 .                  0 6
52  33 0 .                 .                  . .
52  34 0 .                 .                  . .
52  35 0 .                 .                  . .
52  36 0 .                 .                  . .
52  37 0 .                 .                  . .
52  38 0 .                 .                  . .
52  39 0 .                 .                  . .
52  40 0 .                 .                  . .
52  41 0 .                 .                  . .
52  42 0 .                 .                  . .
52  43 0 .                 .                  . .
52  44 0 .                 .                  . .
52  45 0 .                 .                  . .
52  46 0 .                 .                  . .
52  47 0 .                 .                  . .
52  48 0 .                 .                  . .
52  49 0 .                 .                  . .
52  50 0 .                 .                  . .
52  51 0 .                 .                  . .
52  52 0 .                 .                  . .
52  53 0 .                 .                  . .
52  54 0 .                 .                  . .
52  55 0 .                 .                  . .
52  56 0 .                 .                  . .
52  57 0 .                 .                  . .
52  58 0 .                 .                  . .
52  59 0 .                 .                  . .
52  60 0 .                 .                  . .
52  61 0 .                 .                  . .
52  62 0 .                 .                  . .
52  63 0 .                 .                  . .
52  64 0 .                 .                  . .
52  65 0 .                 .                  . .
52  66 0 .                 .                  . .
52  67 0 .                 .                  . .
52  68 0 .                 .                  . .
52  69 0 .                 .                  . .
52  70 0 .                 .                  . .
52  71 0 .                 .                  . .
52  72 0 .                 .                  . .
52  73 0 .                 .                  . .
52  74 0 .                 .                  . .
52  75 0 .                 .                  . .
52  76 0 .                 .                  . .
52  77 0 .                 .                  . .
52  78 0 .                 .                  . .
52  79 0 .                 .                  . .
52  80 0 .                 .                  . .
52  81 0 .                 .                  . .
52  82 0 .                 .                  . .
52  83 0 .                 .                  . .
52  84 0 .                 .                  . .
52  85 0 .                 .                  . .
52  86 3 .                 .                  . .
52  87 3 .                 .                  . .
52  88 3 .             23.25                  . .
52  89 0 3                 . 10.576614379882813 1
52  90 0 3                 . 5.2016143798828125 2
52  91 0 3                 .                  0 3
52  92 0 3                 .                 10 4
52  93 0 3                 .             27.375 5
52  94 0 3                 .              34.75 6
52  95 0 .                 .                  . .
52  96 0 .                 .                  . .
52  97 0 .                 .                  . .
52  98 0 .                 .                  . .
52  99 0 .                 .                  . .
52 100 0 .                 .                  . .
end

In each of the 6 month follow up period, I want to check if the deviation from the base_y is greater than 15/30/40%. The code I was trying to run is:

Code:
tsset id month
bysort id spell_followup (followupmonth): gen var15=((l1.base_y-followup_y)/l1.base_y/>.15) if followupmonth==1
bysort id spell_followup (followupmonth): gen var30=((l1.base_y-followup_y)/l1.base_y/>.30) if followupmonth==1
bysort id spell_followup (followupmonth): gen var50=((l1.base_y-followup_y)/l1.base_y/>.50) if followupmonth==1

But I get an error "not sorted".

Code:
. bysort id spell_followup (followupmonth): gen var15=((l1.base_y-followup_y)/l1.ba
> se_y/>.15) if followupmonth==1
not sorted
r(5);

end of do-file

r(5);
I did try to tsset the data and use bysort. But, I am clearly messing up somewhere but the error doesn't give a lot of detail and I am stuck. I will be grateful for your help.
Sincerely,
Sumedha.