@incollection{iiasa13979,
          series = {Springer Texts in Statistics},
       booktitle = {Applied Mathematical Demography},
         address = {New Yok, USA},
           title = {Heterogeneity and Selection in Population Analysis},
       publisher = {Springer},
             doi = {10.1007/978-1-4757-1879-9\_14},
           pages = {385--399},
            year = {1985},
             url = {https://pure.iiasa.ac.at/id/eprint/13979/},
            isbn = {978-1-4757-1879-9},
            issn = {1431-875X},
        abstract = {Heterogeneity in the underlying population places difficulties in the way of interpretation of all statistical data based on averages. No two persons are equally likely to die in the next year; no two marriages are equally likely to be broken up by divorce; no two businesses are equally likely to fail; no two automobiles are equally likely to break down. That on the average a given make of automobile will travel 50,000 miles without major repairs offers little assurance for any particular automobile. Averages can be applied to individual cases only at great risk. This gross aspect of heterogeneity is not the subject of the present chapter.},
          author = {Keyfitz, N.}
}