public static double LifetimeReturnRateEstimate(DayStyleColorSalesAndReturns returns, int days, IDelayModel distribution)
        {
            var quantityReturned = returns.ReturnedUnits
                .Where(it => it.Delay <= days)
                .Sum(it => it.Units);
            var proportionReturned = (double) quantityReturned;
            if(returns.UnitsSold != 0)
                proportionReturned = (double)quantityReturned / (double)returns.UnitsSold;

            var proportionOfTotalExpected = distribution.ProportionReturnedBy(days);
            var totalReturnRate = proportionReturned / proportionOfTotalExpected;

            return AdjustedReturnRate(totalReturnRate);
        }