Hi all,

For the firms in my sample, I need to calculate the volatility of earnings. However, I keep on failing to do this. Measuring volatility can be done by calculating the st. deviations of the last 4 quarters' ROA numbers. So for example, for the following firm it looks like this:

fyearq fqtr cusip conm atq niq ROA
2012 1 55336V100 MPLX LP 1435.2 30.4 .0021182
2012 2 55336V100 MPLX LP 1501.6 29.8 .0198455
2012 3 55336V100 MPLX LP 1250.2 36.9 .0295153
2012 4 55336V100 MPLX LP 1301.3 28.9 .0222086
2013 1 55336V100 MPLX LP 1311.9 17.6 .0134157
2013 2 55336V100 MPLX LP 1217.7 18.6 .0152747
2013 3 55336V100 MPLX LP 1218.7 21.5 .0176417
2013 4 55336V100 MPLX LP 1208.5 20.2 .0167149
2014 1 55336V100 MPLX LP 1193.7 34.2 .0286504
2014 2 55336V100 MPLX LP 1181.4 28.8 .0243779
2014 3 55336V100 MPLX LP 1194.3 29.1 .0243657
2014 4 55336V100 MPLX LP 1214.5 29.2 .0240428
2015 1 55336V100 MPLX LP 1354 68 .0502216
2015 2 55336V100 MPLX LP 1382.6 75 .0542456
2015 3 55336V100 MPLX LP 1391.1 63 .0452879
2015 4 55336V100 MPLX LP 15677 42 .0026791
2016 1 55336V100 MPLX LP 15978 -14 -.0008762
2016 2 55336V100 MPLX LP 16079 71 .0044157
2016 3 55336V100 MPLX LP 16415 192 .0116966
2016 4 55336V100 MPLX LP 16646 183 .0109936
2017 1 55336V100 MPLX LP 18285 186 .0101723
2017 2 55336V100 MPLX LP 18601 190 .0102145
2017 3 55336V100 MPLX LP 19238 216 .0112278
2017 4 55336V100 MPLX LP 19500 238 .0122051
2018 1 55336V100 MPLX LP 21006 421 .0200419
2018 2 55336V100 MPLX LP 21412 453 .0211564
2018 3 55336V100 MPLX LP 22379 510 .0227892
2018 4 55336V100 MPLX LP 22779 434 .0190526


So what I exactly need is:
- One column added that calculates the st. deviation for the 4 quarters every year.
- When I would have this, I need to change the dataset so that I will have one row for every firm-year combination (so that I can merge this with my other dataset).

Hopefully it is clear what I need and what my problems are, and hopefully someone knows which codes/handlings I need to do!

Kind regards