Biochemigraphy of Aging and Age-Specific Mortality in Drosophila melanogaster

This chapter focuses on the biodemography of aging and age-specific mortality in Drosophila melanogaster. Two approaches are used to describe trends in the (often noisy) data on age-specific mortality. One approach is to apply a nonparametric smoothing procedure. For data organized in the form of a life table, smoothing can be accomplished by widening the age intervals. If times to death for each individual in the sample are known with reasonable accuracy and/or small sample size does not allow construction of a conventional life table, then the method of hazard rate smoothing using kernel functions may be more appropriate. The latter method is computationally more complex, although special routines are available in SAS and Stata. Applying methods of nonparametric smoothing decreases statistical noise and facilitates visual inspection of mortality plots but does not allow quantitative analysis of life-span data. The second major approach for summarizing and simplifying mortality estimates is parametric model fitting that allows researchers to describe the observed mortality kinetics using a small number of parameters of a specified mortality model.