External to the model, the IFs project calculated an initial ratio of YLD to YLL based on data from the World Health Organization.  Those ratios are regional but specific to cause of death category. In the base year of the model, IFs initializes the value for YLDs by applying this ratio to YLL.  In subsequent years IFs calculates the growth rate for mortality  from the previous year and uses that to forecast the change in morbidity.  The percentage decline in disability relative to decline in mortality can be controlled by the parameter ( hlmorbtomortgthport ).  IFs estimates YLD from the ratio of regional morbidity to mortality (YLD/YLL). This ratio is used for initialization and then the growth rate for mortality is computed and applied to forecast morbidity. Morbidity results can then be adjusted with a multiplier ( hlmorbtomortgthport ) that can be handled by the user across time. This multiplier is specific for each subtype, with default values detailed in the table below.  As an example, the value of 50 percent for cardiovascular disease  ( hlmorbtomortgthport =0.5) suggests that morbidity decreases at half the rate of mortality.  Because malaria is set at 100 percent ( hlmorbtomortgthport =1.0), morbidity will change at exactly the same rate as mortality; a higher value for the parameter could be used to represent a situation in which morbidity declined faster than mortality.

Percentage decline in disability relative to decline in mortality 

Once morbidity is computed, the calculations to find YLDs (HLYLD) are identical to those for YLLs (HLYLL)–using morbidity instead of mortality to compute the number of people affected by a given disease.  HLYLDWORK again focuses only on the population aged between 20 and 64.

Morbidity related to mental health is the one exception to the above methodology.  IFs computes an initial ratio of YLD/POP based on WHO data, keeping the ratio constant over time.