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SUMMARY:Estimation of time to pregnancy from current duration data - Niels
  Keiding\, Department of Biostatistics\, University of Copenhagen
DTSTART:20091027T143000Z
DTEND:20091027T153000Z
UID:TALK20468@talks.cam.ac.uk
CONTACT:Michael Sweeting
DESCRIPTION:Time to pregnancy is the duration from a couple starts trying 
 to become pregnant until they succeed and is considered one of the most di
 rect methods to measure natural fecundity in humans. Statistical tools for
  designing and analysing time to pregnancy studies belong to the general a
 rea of survival analysis\, but several special features require special at
 tention. We focus here on starting from a cross-sectional sample of couple
 s currently trying to become pregnant\, using current duration as basis fo
 r estimation. This corresponds to using the backward recurrence time as ba
 sis for the inference\, and here the preferable statistical model turns ou
 t to be the accelerated failure time model.\n\nThe inference is quite sens
 itive to observations near zero\; indeed Woodroofe and Sun pointed out tha
 t the nonparametric maximum likelihood estimator is inconsistent at zero. 
 Switching to parametric models\, we are faced with balancing between stabi
 lity or flexibility. The former represented by a simple mixed exponential 
 model such as the Pareto distribution\, the latter by a much larger class 
 of distributions suggested by Yamaguchi in a sociological context.\n\nWe a
 re collaborating with a group of epidemiologists\, statisticians and demog
 raphers in France where we have helped design and analyze a large telephon
 e survey among French women based on the current duration approach. The ta
 lk will briefly mention several practical features that one has to take in
 to account but we will focus on the statistical problems and present vario
 us simulation studies highlighting the sensitivity problems.\n\nReferences
 :\n\nKeiding\, N.\, Kvist\, K.\, Hartvig\, H.\, Tvede\, M. & Juul\, S. (20
 02). Estimating time to pregnancy from current durations in a cross-sectio
 nal sample. Biostatistics 3\, 565-578.\n\nScheike\, T. & Keiding\, N. (200
 6). Design and analysis of time to pregnancy. Stat. Meth. Med. Res. 15\, 1
 27-140.\n\nSlama\, R.\, Ducot\, B.\, Carstensen\, L.\, Lorente\, C.\, de L
 a Rochebrochard\, E.\, Leridon\, H.\, Keiding\, N. & Bouyer\, J.(2006). Fe
 asibility of the current duration approach to study human fecundity. Epide
 miology 17\, 440-449.
LOCATION:Large Seminar Room\, 1st Floor\, Institute of Public Health\, Uni
 versity Forvie Site\, Robinson Way\, Cambridge
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