Dear Statalist forum,

I would like to ask the following. I have a time series with missing data for certain years, and I would like to calculate the growth rate for the variable median for each year based on a specific base year (the first year for which data for median is available). In other words, I would like create an index series for the median variable (base year=100). I have calculated the growth rate of median using log first differences, where the code looks as follows:
Code:
gen logmedian=log(median)
gen growthmedian= logmedian[_n] - logmedian[_n-1] ///
if country[_n] == country[_n-1]
Which gives me the growth rate of median illustrated in the data example below.

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str38 country double year float PPPrealgdi double(gdpcap hhexp median) float(logmedian growthmedian)
"Brazil" 1981             .                 .                .            1531.68  7.33412           .
"Brazil" 1982             .                 .                . 1541.3999999999999 7.340446  .006326199
"Brazil" 1983             .                 .                .            1266.72 7.144186  -.19626045
"Brazil" 1984             .                 .                . 1275.3600000000001 7.150984   .00679779
"Brazil" 1985             .                 .                . 1454.6399999999999 7.282514   .13152981
"Brazil" 1986             .                 .                .            2435.64 7.797965   .51545143
"Brazil" 1987             .                 .                . 1858.3200000000002 7.527428   -.2705369
"Brazil" 1988             .                 .                .            1741.08 7.462261  -.06516743
"Brazil" 1989             .                 .                .            1877.16 7.537515   .07525444
"Brazil" 1990             . 10344.86438961035 720147699317.049 1616.3999999999999 7.387957  -.14955854
"Brazil" 1991             . 10319.92933521456  779750705063.36                  .        .           .
"Brazil" 1992             . 10099.77561998418 774717151172.519            1625.52 7.393583           .
"Brazil" 1993             . 10398.16035761199 809876320756.008            1670.88 7.421106   .02752304
"Brazil" 1994             . 10776.43311211532 870158244588.953                  .        .           .
"Brazil" 1995   8.49598e+11  11072.7252903522 945180706038.132 2219.3999999999996 7.704992           .
"Brazil" 1996  8.860042e+11 11137.58926300037 974140377103.669            2253.48 7.720231  .015238762
"Brazil" 1997  9.292225e+11 11334.82075340726 1003685800287.16            2228.88 7.709254  -.01097679
"Brazil" 1998  9.614585e+11 11197.70193788836 996459125418.385            2311.44 7.745626  .036371708
"Brazil" 1999  9.802891e+11 11081.65462053813 1000228307626.96            2222.04 7.706181  -.03944492
"Brazil" 2000  9.933006e+11 11370.97093925103 1040563838430.28                  .        .           .
"Brazil" 2001   9.76703e+11 11368.46644957097 1048589775648.83            2529.36 7.835721           .
"Brazil" 2002 1.0052062e+12 11559.56059660686 1062419071054.17               2562 7.848544   .01282215
"Brazil" 2003  1.016476e+12 11541.97503234461 1056618339648.85 2492.2799999999997 7.820953 -.027590275
"Brazil" 2004 1.1615509e+12  12058.2077119511 1098074697769.69            2569.32 7.851397   .03044319
"Brazil" 2005 1.1970837e+12 12298.58794846535 1146630208256.88 2717.7599999999998 7.907563   .05616665
"Brazil" 2006 1.2698414e+12 12643.56500898064 1207226170587.02            2960.64 7.993161   .08559752
"Brazil" 2007  1.374465e+12 13268.41390244003 1284202177161.98            3172.32 8.062219   .06905794
"Brazil" 2008 1.4525213e+12 13802.81799242376 1367216409264.71            3394.44 8.129894   .06767559
"Brazil" 2009 1.5419716e+12 13649.86584029567 1428144990218.13            3544.68 8.173203   .04330921
"Brazil" 2010  1.787638e+12 14537.56719309033 1517109456849.07                  .        .           .
"Brazil" 2011 1.9028176e+12 14973.09847367468 1590210762172.73            3903.12 8.269531           .
"Brazil" 2012 2.0173075e+12 15119.91213817678  1645859403527.4            4244.76  8.35344   .08390903
"Brazil" 2013 2.1333167e+12 15432.89363081413  1702987902524.9             4472.4 8.405681   .05224037
"Brazil" 2014 2.2029756e+12  15374.2615071807 1741310567302.85            4621.08 8.438384    .0327034
"Brazil" 2015 2.1500094e+12 14702.59126803164 1685301439554.04 4398.4800000000005 8.389014  -.04936981
"Brazil" 2016             . 14077.12140855444 1612150747594.78                  .        .           .
"Brazil" 2017             . 14103.45153134036 1627686451678.68                  .        .           .
end
Having calculated my growth rate, I am not sure now how to proceed to obtain the index series for median, one that also takes into account the missing data for the growthmedian variable. If anyone has any suggestions on how to do this, I would greatly appreciate it.

Thank you for your time.

Best,

Ryan