Make a normalised distribution

[Federico Nutarelli]

Hi all,

I have elaborated data in the following way:

* Example generated by -dataex-. To install: ssc install dataex
clear
input double ann_sales float(normalized_year id_prd_firm)
              85 1  1
           238.5 2  1
            47.5 1  2
             211 2  2
           395.5 3  2
               5 1  3
            35.5 2  3
              79 3  3
4.89489170623635 1  4
20.4661130821099 2  4
  34.15046726974 3  4
60.1198185908836 4  4
             3.8 1  5
35.7852796805447 2  5
64.9362551878901 3  5
104.563615293974 4  5
140.115426731404 5  5
          .08625 1  6
3.19348247881494 2  6
13.8844777666676 3  6
32.2297332153678 4  6
  50.11621009883 5  6
 12.603100897487 1  7
32.1184017273114 2  7
51.7176325634169 3  7
71.7845568557696 4  7
91.1086552100052 5  7
               . 1  8
3.38420086365568 2  8
9.38822442256267 3  8
16.6845568557696 4  8
20.1086552100052 5  8
19.2733698657207 1  9
40.1001733426185 2  9
74.1621516948018 3  9
               . 1 10
20.0500866713092 2 10
55.6216137711013 3 10
24.9655924897466 1 11
95.8230756038792 2 11
               . 1 12
.968500631060278 2 12
3.95838831999946 3 12
 8.3867519780248 4 12
12.3776620743859 5 12
               . 1 13
 3.6963815341215 2 13
 23.775420922626 3 13
41.0192047740423 4 13
 76.442165129007 5 13
111.523673566708 6 13
         14.5016 1 14
        111.3812 2 14
         221.184 3 14
        419.6482 4 14
           29.88 1 15
        114.9016 2 15
        315.9248 3 15
        478.5258 4 15
25.3613967219308 1 16
131.957309050535 2 16
327.845598168762 3 16
101.085129145652 1 17
163.527433898824 2 17
230.187987161852 3 17
 294.79443680269 4 17
4.76666666666667 1 18
48.3782684739834 2 18
98.8616623577295 3 18
179.960540622671 4 18
289.073722474105 5 18
        126.7898 1 19
 416.98599120078 2 19
695.595411625484 3 19
       12.196876 1 20
       54.323206 2 20
       110.34172 3 20
        182.9958 4 20
       247.70248 5 20
       7.3166667 1 21
       108.17194 2 21
       300.77331 3 21
       496.01326 4 21
        .5139008 1 22
       15.859942 2 22
       34.314289 3 22
       49.616878 4 22
       3.1143158 1 23
       31.499274 2 23
       65.290581 3 23
       8.9761325 1 24
        45.59026 2 24
71.6790739815622 1 25
362.627567148668 2 25
9.73333333333333 1 26
11.2666666666667 2 26
          12.985 1 27
           19.68 2 27
         37.3725 3 27
              20 1 28
end

my aim is to plot the distribution (trend) of sales from the launch year (here normalized_year = 1). Any idea on how to do that?
I am actually struggling in understanding how to do it.