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1994-10-25
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Document 2320
DOCN M94A2320
TI Segmented Cox models can distinguish short and long term AIDS
progression markers.
DT 9412
AU Fore AJ; Kramer A; Grund B; Hannan P; University of Minnesota.
SO Int Conf AIDS. 1994 Aug 7-12;10(1):330 (abstract no. PC0256). Unique
Identifier : AIDSLINE ICA10/94370255
AB OBJECTIVE: We studied the time-varying effects of CD4+ T-lymphocytes
(CD4), immunoglobin A (IgA), and phytohaemagglutinin (PHA) on the
development of AIDS. We used segmented Cox models to estimate the short
and long term effects of the baseline covariates. METHODS: Using
illustrative data from a longitudinal study, we examined 155
HIV-seropositive homosexual or bisexual men with complete baseline
information on the covariates under study. During the observation
period, 50 men (32%) developed AIDS. Predictors of AIDS were first
evaluated using traditional Cox model methods. We then estimated the
contribution of the covariates to the hazard at each time point with
Aalen's nonparametric linear regression model. An 'Aalen plot' was
constructed by plotting the cumulative hazard function against time.
From inspection of Aalen plots and the distribution of events, a break
point of 1100 days was chosen for the segmented Cox models. Parameters
in each segment (before and after 1100 days) were estimated. RESULTS: In
traditional Cox analysis for the entire observation period, all
covariates were significant predictors of progression. Using the
segmented model for the first 1100 days, significant predictors were CD4
(p = .048) and PHA (p = .007); IgA was marginally significant (p =
.079). In the second segment, only CD4 was significant (p = .017).
DISCUSSION AND CONCLUSIONS: In contrast to the traditional Cox model,
the segmented Cox model enables us to investigate the possibly changing
importance of baseline covariates over time. The Aalen plot provides a
visual indication of time dependency and can suggest a suitable break
point for segmented Cox models. Using these methods, short and long term
predictors of AIDS progression can be identified. CD4, IgA, and PHA are
all good short term predictors of AIDS. The predictive effect of
baseline IgA and PHA appears to decay after approximately three years.
Only CD4, a well established prognostic factor, is an important long
term predictor.
DE Acquired Immunodeficiency Syndrome/DIAGNOSIS/EPIDEMIOLOGY/ *IMMUNOLOGY
Adult Bisexuality/STATISTICS & NUMER DATA Homosexuality/STATISTICS &
NUMER DATA Human HIV Infections/DIAGNOSIS/EPIDEMIOLOGY/*IMMUNOLOGY
IgA/*BLOOD Longitudinal Studies Lymphocyte Transformation/*IMMUNOLOGY
Male Models, Statistical Prognosis Proportional Hazards Models T4
Lymphocytes/*IMMUNOLOGY MEETING ABSTRACT
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).