Adam Lenart | University of Southern Denmark (original) (raw)

Papers by Adam Lenart

Aging Cell, 2015

An epigenetic profile defining the DNA methylation age (DNAm age) of an individual has been sugge... more An epigenetic profile defining the DNA methylation age (DNAm age) of an individual has been suggested to be a biomarker of aging, and thus possibly providing a tool for assessment of health and mortality. In this study, we estimated the DNAm age of 378 Danish twins, age 30-82 years, and furthermore included a 10-year longitudinal study of the 86 oldest-old twins (mean age of 86.1 at follow-up), which subsequently were followed for mortality for 8 years. We found that the DNAm age is highly correlated with chronological age across all age groups (r = 0.97), but that the rate of change of DNAm age decreases with age. The results may in part be explained by selective mortality of those with a high DNAm age. This hypothesis was supported by a classical survival analysis showing a 35% (4-77%) increased mortality risk for each 5-year increase in the DNAm age vs. chronological age. Furthermore, the intrapair twin analysis revealed a more-than-double mortality risk for the DNAm oldest twin compared to the co-twin and a 'dose-response pattern' with the odds of dying first increasing 3.2 (1.05-10.1) times per 5-year DNAm age difference within twin pairs, thus showing a stronger association of DNAm age with mortality in the oldest-old when controlling for familial factors. In conclusion, our results support that DNAm age qualifies as a biomarker of aging.

SSRN Electronic Journal, 2000

ENEPRI Research Reports publish the original research results of projects undertaken in the conte... more ENEPRI Research Reports publish the original research results of projects undertaken in the context of an ENEPRI project. This paper was prepared as part of the Adequacy of Old-Age Income Maintenance in the EU (AIM) project -which has received financing from the European Commission under the 6 th Research Framework Programme (contract no. SP21-CT-2005-513748). The views expressed are attributable only to the authors and not to any institution with which they are associated.

Mpidr Working Papers, 2012

The Gompertz distribution is widely used to describe the distribution of adult deaths. Previous w... more The Gompertz distribution is widely used to describe the distribution of adult deaths. Previous works concentrated on formulating approximate relationships to characterize it. However, using the generalized integro-exponential function exact formulas can be derived for its moment-generating function and central moments. Based on the exact central moments, higher accuracy approximations can be defined for them. In demographic or actuarial applications, maximum-likelihood estimation is often used to determine the parameters of the Gompertz distribution. By solving the maximum-likelihood estimates analytically, the dimension of the optimization problem can be reduced to one both in the case of discrete and continuous data.

Scandinavian Actuarial Journal, 2014

The census documents from Roman Egypt form the best documentary source of demographic information... more The census documents from Roman Egypt form the best documentary source of demographic information for the Roman Empire. Earlier collections (Bagnall and Frier 2006; Bagnall, Frier, and Rutherford 1997) have shown that some individuals and households appear more than once within
this body of evidence. This article demonstrates how semi-automated record linkage provides an efficient and systematic way of producing linkages between early historical documentary sources that are fragmentary. The process yielded more linkages with generally high probability values than previously employed linkage-by-hand methods. As the added examples show, semi-automated record linkage also proved to be a useful method to fill gaps in papyri by transferring information from one record to the other. As such, it provides new opportunities for papyrologists and epigraphers working with fragmented materials pertaining to the ancient Greco-Roman world.

Adult mortality decline was the driving force of life-expectancy increase in many developed count... more Adult mortality decline was the driving force of life-expectancy increase in many developed countries in the second half of the twentieth century. In this paper we study one of the most widely used models to capture adult human mortality - the Gompertz proportional hazards model. In its standard settings we, first, derive analytic expressions for period and cohort life expectancy.

International Encyclopedia of the Social & Behavioral Sciences, 2015

Theoretical Population Biology, 2013

In a population of individuals, whose mortality is governed by a Gompertz-Makeham hazard, we deri... more In a population of individuals, whose mortality is governed by a Gompertz-Makeham hazard, we derive closed-form solutions to the life-expectancy integral, corresponding to the cases of homogeneous and gamma-heterogeneous populations, as well as in the presence/absence of the Makeham term. Derived expressions contain special functions that aid constructing high-accuracy approximations, which can be used to study the elasticity of life expectancy with respect to model parameters. Knowledge of Gompertz-Makeham life expectancies aids constructing life-table exposures.

Demographic Research, 2011

In a Gompertz mortality model with constant yearly improvements at all ages, linear increases in ... more In a Gompertz mortality model with constant yearly improvements at all ages, linear increases in period life expectancy correspond to linear increases in the respective cohort life expectancy. The link between the two measures can be given by a simple approximate relationship.

Communications in Statistics - Theory and Methods, 2016

While the Gompertz distribution is often fitted to lifespan data, testing whether the fit satisfi... more While the Gompertz distribution is often fitted to lifespan data, testing whether the fit satisfies theoretical criteria is being neglected. Here four goodness-of-fit measures -the Anderson-Darling statistic, the correlation coefficient test, a statistic using moments, and a nested test against the generalized extreme value distributions -are discussed. Along with an application to laboratory rat data, critical values calculated by the empirical distribution of the test statistics are also presented.

Demographic Research, 2015

BACKGROUND The Gompertz force of mortality (hazard function) is usually expressed in terms of a, ... more BACKGROUND The Gompertz force of mortality (hazard function) is usually expressed in terms of a, the initial level of mortality, and b, the rate at which mortality increases with age. OBJECTIVE We express the Gompertz force of mortality in terms of b and the old-age modal age at death M and present similar relationships for other widely-used mortality models. Our objective is to explain the advantages of using the parameterization in terms of M. METHODS Using relationships among life table functions at the modal age at death, we derive the Gompertz force of mortality as a function of the old-age mode. We estimate the correlation between the estimators of old (a and b) and new (M and b) parameters from simulated data. RESULTS When the Gompertz parameters are statistically estimated from simulated data, the correlation between estimated values of b and M is much less than the correlation between a and b. For the populations in the Human Mortality Database there is a negative association between a and b and a positive association between M and b. CONCLUSIONS Using M, the old-age mode, instead of a, the level of mortality at the starting age, has two major advantages. First, statistical estimation is facilitated by the lower correlation between the estimators of model parameters. Second, estimated values of M are more easily comprehended and interpreted than estimated values of a.