Homogeneous
\ˌhoʊməˈʤiniəs\
Homogeneous means ‘containing identical items’, or ‘displaying identical characteristics’.
In an analysis of mortality and longevity statistics, it is generally desirable to sub-divide a given population into ‘relatively homogeneous’ groups where each group displays similar characteristics in relation to their life expectancy.
For example, splitting populations into sub-groups by age and by gender makes the sub-groups more homogeneous than the whole population. Splitting the sub-groups according to whether they are/were smokers (for example) would make the groups yet more homogeneous. Absolute homogeneity is generally impossible in populations of people as no two individuals are truly identical.