sum stdev

[#1]

I have the following formula. It takes the stdev of fund return for the last three years. Now I need to sum the result of the formula. I tried sum  and aggr(sum)) none of which seem to work. It either returns 0 or null.

stdev(  {<dte_monthname={'>$(=date((max(dte_monthname))-365*3,'YYYY-MM-DD')) <=$(=date(max(dte_monthname),'YYYY-MM-DD'))'}>} aggr(

            sum( weighted_net_profit) /sum(market_system_weight_current_normalized) , dte_monthname ))