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Comment
. 2015 Nov:145:125-8.
doi: 10.1016/j.socscimed.2015.07.013. Epub 2015 Jul 31.

Clarifying hierarchical age-period-cohort models: A rejoinder to Bell and Jones

Eric N Reither  1 , Kenneth C Land  2 , Sun Y Jeon  3 , Daniel A Powers  4 , Ryan K Masters  5 , Hui Zheng  6 , Melissa A Hardy  7 , Katherine M Keyes  8 , Qiang Fu  9 , Heidi A Hanson  10 , Ken R Smith  11 , Rebecca L Utz  12 , Y Claire Yang  13
Affiliations
Comment

Clarifying hierarchical age-period-cohort models: A rejoinder to Bell and Jones

Eric N Reither et al. Soc Sci Med. 2015 Nov.

Abstract

Previously, Reither et al. (2015) demonstrated that hierarchical age-period-cohort (HAPC) models perform well when basic assumptions are satisfied. To contest this finding, Bell and Jones (2015) invent a data generating process (DGP) that borrows age, period and cohort effects from different equations in Reither et al. (2015). When HAPC models applied to data simulated from this DGP fail to recover the patterning of APC effects, B&J reiterate their view that these models provide "misleading evidence dressed up as science." Despite such strong words, B&J show no curiosity about their own simulated data--and therefore once again misapply HAPC models to data that violate important assumptions. In this response, we illustrate how a careful analyst could have used simple descriptive plots and model selection statistics to verify that (a) period effects are not present in these data, and (b) age and cohort effects are conflated. By accounting for the characteristics of B&J's artificial data structure, we successfully recover the "true" DGP through an appropriately specified model. We conclude that B&Js main contribution to science is to remind analysts that APC models will fail in the presence of exact algebraic effects (i.e., effects with no random/stochastic components), and when collinear temporal dimensions are included without taking special care in the modeling process. The expanded list of coauthors on this commentary represents an emerging consensus among APC scholars that B&J's essential strategy--testing HAPC models with data simulated from contrived DGPs that violate important assumptions--is not a productive way to advance the discussion about innovative APC methods in epidemiology and the social sciences.

Keywords: Age–period–cohort models; Body mass index; Cohort effects; Hierarchical modeling; Obesity epidemic; Random effects; Simulation models; Social change.

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Figures

Fig. 1
Fig. 1
Descriptive estimates of obesity prevalence by age, period and birth cohort in 100 datasets simulated from the DGP invented by B&J (median estimates in bold).
Fig. 2
Fig. 2
Estimates from quadratic age–cohort models applied to data simulated from the DGP invented by B&J, with 95% point intervals in shaded areas.
See this image and copyright information in PMC

Comment on

References

    1. Bell A, Jones K. Should age-period-cohort analysts accept innovation without scrutiny? A response to Reither, Masters, Yang, Powers, Zheng and Land. Soc Sci Med. 2015;128:331–333. - PubMed
    1. R Core Team. R Foundation for Statistical Computing; Vienna, Austria: 2015. R: A Language and Environment for Statistical Computing. http://www.R-project.org.
    1. Reither EN, Masters RK, Yang YC, Powers DA, Zheng H, Land KC. Should age-period-cohort studies return to the methodologies of the 1970s? Soc Sci Med. 2015;128:356–365. - PMC - PubMed