Inferring the demographic history from DNA sequences: An importance sampling approach based on non-homogeneous processes.

In Ait Kaci Azzou et al. (2015) we introduced an Importance Sampling (IS) approach for estimating the demographic history of a sample of DNA sequences, the skywis plot. More precisely, we proposed a new nonparametric estimate of a population size that changes over time. We showed on simulated data that the skywis plot can work well in typical situations where the effective population size does not undergo very steep changes. In this paper, we introduce an iterative procedure which extends the previous method and gives good estimates under such rapid variations. In the iterative calibrated skywis plot we approximate the effective population size by a piecewise constant function, whose values are re-estimated at each step. These piecewise constant functions are used to generate the waiting times of non homogeneous Poisson processes related to a coalescent process with mutation under a variable population size model. Moreover, the present IS procedure is based on a modified version of the Stephens and Donnelly (2000) proposal distribution. Finally, we apply the iterative calibrated skywis plot method to a simulated data set from a rapidly expanding exponential model, and we show that the method based on this new IS strategy correctly reconstructs the demographic history.

The reliability of the maternal memory in a retrospective assessment of nutritional status.

This study raises the question of the validity of conclusions based on recalled data by testing the maternal ability to report vital events on her newborn infant after 8 years. First, the retrospective information given by the mother was compared to the prospective data collected immediately after birth. Second, the validity of statistical analyses based on retrospective data was discussed. A dispersion model was used and discrepancies were found between the two sets of data collected in two different ways on the same subjects. It was concluded that the use of retrospective information can lead to false results in regression analyses and could invalidate comparisons in case-control studies because of the difference in variability between cases and controls.

Parental age and birth order in Alzheimer's disease: a case-control study in the Saguenay-Lac-St-Jean area (Quebec, Canada).

Parental age at the time of birth of 133 clinically diagnosed Alzheimer patients from the Saguenay-Lac-St-Jean area (Quebec, Canada) were compared with those of 6 control groups formed out a population registry. The birth order of the Alzheimer patients was also analyzed. The results did not show any parental age or birth order effect, which is in agreement with previous reports. The importance of control selection in such studies is stressed.

Canadian projections of cases suffering from Alzheimer's disease and senile dementia of Alzheimer type over the period 1986-2031.

Alzheimer's disease (AD) is characterized by irreversible changes in cognitive and intellectual functions, accompanied by progressive memory loss, and described by neurochemical and neuropathological impairments. The classic term Alzheimer's disease applies to presenile dementia, while all of the syndromes that share the distinctive signs of AD are known as senile dementia of the Alzheimer type (SDAT). In Canada, as in several other industrialized countries, we are seeing a rapid growth of the elderly population. The renewed interest in AD and SDAT is partly attributable to the view that the increasing percentage of sufferers will have a significant socioeconomic impact. Few attempts have been made to project the number of cases of SDAT in Canada. In assessing the prevalence of SDAT in an over 65 population, a rate of 2.5% (or 3%) is commonly applied. This rate corresponds to one half the estimated prevalence rate for all severe types of dementia, using an average of the rates arrived at by some ten studies. The authors dispute this approach: i. the assumption that 50% of dementia cases will be AD is not verified for all populations; ii. the use of a single prevalence rate for everyone over age 65 is rather uninformative; and iii. the combining of results from various sources is questionable given the possible lack of consistency in the following respects: diagnostic criteria, methods of investigation, effort made to recruit cases, and representativeness of the groups studied. In this article, prevalence rates by age group have been inferred based on two Finnish studies conducted in the 1980s on the prevalence of AD in the general population.(ABSTRACT TRUNCATED AT 250 WORDS)