how to compute RSI monthly based

[ArthMizz]

Hi,

I am trying to compute the Relative Strengh Index (RSI) of 500 stocks but on a monthly basis. I wrote the following code based on a paper found online, however, there are some mistakes but I do not know how to fix them. Moreover, there are some statements that I do not understand what "%do i=16 %to 7570;" stand for in the code.

data Project.MonthlyPrice;
    set RSI;
    by PERMNO;
    lprc = lag(prc);
    if prc>lprc then gain = prc-lprc;
    if prc<lprc then loss = lprc-prc;
    if first.PERMNO then do;
  gain = .;
  loss = .;
    end;
    retain months 0;
    months+1;
    if first.PERMNO then months = 1;
    if gain = . then gain = 0;
    if loss = . then loss = 0;
    retain sumgain 0;
    sumgain = sumgain + gain;
    retain sumloss 0;
    sumloss = sumloss + loss;
    if months=15 then do;
        AveGain = (sumgain-gain) / 14;
 AveLoss = (sumloss-loss) / 14;  
 RS =  AveGain / AveLoss;
 RSI = 100-100/(1+RS);
    end;
    drop sumgain sumloss;
run;
%macro calRSI();
    %do i=16 %to 7570;
        data Project.MonthlyPrice;
     set RSI;
     lAveGain = lag1(AveGain);
     lAveLoss = lag1(AveLoss);
     if months = &i then do;
         AveGain = (lAveGain*13+gain)/14;
  AveLoss = (lAveLoss*13+loss)/14;
  RS =  AveGain / AveLoss;
  RSI = 100-100/(1+RS);
     end;
    %end;
%mend;
data Project.MonthlyPrice;
    set RSI;
run;

Thank in advance

[PeterClemmensen]

Please provide a link to the paper and some example data. Makes it a lot easier to help you.

[ArthMizz]

here's the link to the paper: http://support.sas.com/resources/papers/proceedings12/163-2012.pdf

I am using CRSP from WRDS Monthly stock return and S&P500 returns in my dataset. I used the past 10 years of data (from December 2007 to December 2017) and the entire database (almost 7200 stocks).