Cohorts are people sharing a similar experience or event at a particular time. For example all children born in a particular place and time, or all students graduating from high school in a particular place and time are cohorts. Cohorts are frequently used in longitudinal research. Marvin Wolfgang, for example, established a research project to follow all male children born in Philadelphia in 1940 in order to determine their encounters with the police.
Identification of Parameters in Cohort Models - WOLFGANG JAGODZINSKI, Sociological Methods & Research, Vol. 12, No. 4, 375-398 (1984) - Linear-additive age-period cohort models that permit the maximum number of aging effects, period effects, and cohort effects, full cohort models, are underidentified. In this article, some general rules will be given for detecting identified and underidentified parameters in any full cohort model under zero-sum restrictions.
It will be demonstrated that only one parameter in a dimension is identified whenever the number of parameters in this dimension is uneven. Otherwise, no parameter is identified. Full cohort models for larger tables contain more overidentifying restrictions, but the number of identified parameters never exceeds four.
Cleavage and Ideological Voting in Age Cohorts
- van der Brug, Wouter. Paper presented at the annual meeting of the MPSA Annual National
Conference
Abstract: This study compares the effects of religion,
social class and left-right on
party choice between EU countries, over 15 years and between generations. Generational
replacement leads to a decreasing effect of long-term determinants of the vote.
Advances in Age–Period–Cohort Analysis
- Herbert L. Smith, University of Pennsylvania, Philadelphia, Sociological Methods &
Research, Vol. 36, No. 3, 287-296 (2008)
Social indicators and demographic rates are often arrayed over time by age. The patterns
of rates by age at one point in time may not reflect the effects associated with aging,
which are more properly studied in cohorts. Cohort succession, aging, and period-specific
historical events provide accounts of social and demographic change. Because cohort
membership can be defined by age at a particular period, the statistical partitioning of
age from period and cohort effects focuses attention on identifying restrictions. When
applying statistical models to social data, identification issues are ubiquitous, so some
of the debates that vexed the formative literature on age–period– cohort models
can now be understood in a larger context. Four new articles on
age–period–cohort modeling call attention to the multilevel nature of the
problem and draw on advances in methods including nonparametric smoothing, fixed and
random effects, and identification in structural or causal models.
Secondary sex ratios and male lifespan: Damaged
or culled cohorts
Ralph Catalano and Tim Bruckner, School of Public Health, University of California
Abstract: Population stressors reportedly reduce the human secondary sex ratio (i.e., the
odds of a newborn's being male) by, among other mechanisms, inducing the spontaneous
abortion of males who would have been born live had mothers not been stressed. Controversy
remains as to whether these abortions result from reduced maternal tolerance of males at
the low end of a relatively constant distribution of survivability (i.e., the “culled
cohort” explanation) or from shifts in the whole distribution of survivability such
that more males fall below a relatively constant criterion of maternal tolerance for low
survivability (i.e., the “damaged cohort” explanation). These alternatives make
opposing predictions regarding the relationship between the secondary sex ratio and
lifespan of male birth cohorts. We test the hypothesis that the secondary sex ratio among
Swedish cohorts born in the years 1751 through 1912 predicts male cohort life expectancy
at birth (i.e., realized lifespan). Our results support the culled cohort argument.
Three-year incidence of AIDS in five cohorts of HTLV-III-infected risk group
members
JJ Goedert, RJ Biggar, SH Weiss, ME Eyster, M Melbye, S Wilson, HM Ginzburg, RJ Grossman,
RA DiGioia, WC Sanchez, and al. et
The incidence of the acquired immune deficiency syndrome (AIDS) among persons infected
with human T-lymphotropic virus type III (HTLV-III) was evaluated prospectively among 725
persons who were at high risk of AIDS and had enrolled before October 1982 in cohort
studies of homosexual men, parenteral drug users, and hemophiliacs. A total of 276 (38.1
percent) of the subjects were either HTLV-III seropositive at enrollment or developed
HTLV-III antibodies subsequently. AIDS had developed in 28 (10.1 percent) of the
seropositive subjects before August 1985. By actuarial survival calculations, the 3-year
incidence of AIDS among all HTLV-III seropositive subjects was 34.2 percent in the cohort
of homosexual men in Manhattan, New York, and 14.9 percent (range 8.0 to 17.2 percent) in
the four other cohorts. Out of 117 subjects followed for a mean of 31 months after
documented seroconversion, five (all hemophiliacs) developed AIDS 28 to 62 months after
the estimated date of seroconversion, supporting the hypothesis that there is a long
latency between acquisition of viral infection and the development of clinical AIDS. This
long latency could account for the significantly higher AIDS incidence in the New York
cohort compared with other cohorts if the virus entered the New York homosexual population
before it entered the populations from which the other cohorts were drawn.
GenomEUtwin Scientific Meeting. European Network of Twin Registries and MORGAM
Cohorts. - Istituto Superiore di Sanit�. Rome, 13-14 December 2004. Abstract
book.
Edited by Maria Antonietta Stazi and Valeria Patriarca 2004, v, 76 p. ISTISAN Congressi
04/C7 Twin cohorts provide a unique competitive advantage for investigations of the role
of genetics and environment or life style in the aetiology of common diseases. This
workshop provides an up-to-date on research within the GenomEUtwin Project (Genome-wide
analysis of European twin and population cohorts to identify genes predisposing to common
diseases) supported by the European Commission under the 5th Framework Programme. The
project has developed and applied to twin and MORGAM (MOnica Risk Genetics Archiving and
Monograph) cohorts new molecular technologies and statistical strategies to define and
characterise the genetic, environmental and life-style risk factors of obesity, migraine,
coronary heart disease and stroke, which represent major health care problems worldwide.
Hospital Readmission Rates for Cohorts of Medicare Beneficiaries in Boston and New
Haven - Elliott S. Fisher, John E. Wennberg, Therese A. Stukel, and Sandra M.
Sharp
Methods We used Medicare claims data to study cohorts of Medicare beneficiaries 65 years
of age or older and residing in Boston or New Haven who were initially hospitalized for
one of five indications (acute myocardial infarction, stroke, gastrointestinal bleeding,
hip fracture, or potentially curative surgery for breast, colon, or lung cancer).
Residents of Boston or New Haven who were discharged between October 1, 1987, and
September 30, 1989, were enrolled in the cohort corresponding to the earliest such
admission and followed for up to 35 months.
Results The relative rate of readmission in Boston as compared with New Haven was 1.64 (95
percent confidence interval, 1.53 to 1.76) for all cohorts combined, with a similarly
elevated rate for each of the five clinical cohorts and each age, sex, and race subgroup
examined.