Dear Statalist Community,

I'm currently analysing abnormal returns using company financials.
In computing a needed leverage variable I encounter some trouble

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input float(date year) double(f_yr f_yr_end) float leverage double(dlc dltt tot_assets)
531 2004 2003 4  .4638955 1.293 27.411 61.876
543 2005 2004 4 .46489215 1.175 25.355 57.067
555 2006 2005 4  .4284869 1.167  21.29  52.41
567 2007 2006 4  .4560486 1.035 25.139 57.393
579 2008 2007 4  .3888294  .632  19.71 52.316
591 2009 2008 4  .4533853  .567 19.221 43.645
603 2010 2009 4 .15166536  .271   5.94 40.952
615 2011 2010 4 .23005947  .334    5.7 26.228
end
format %tm date
format %ty year
Where,
date = current month/year
year = current year
f_yr = current fiscal year
f_yr_end = current fiscal year ending month
dlc = short term debt
dltt = long term debt
tot_assets = total assets

The leverage values have currently been calculated as:
(dlc+dltt)/tot_assets

However, they need to be calculated using the values of dlc, dltt and tot_assets in the previous fiscal year (f-1):

Leveragek,t= (dlck,f-1+dlttk,f-1)/tot_assetsk,f-1

for firm k in year t

How can I accomplish this?

Thank you in advance!