[abstract] RATIONAL DECOMPRESSION TRIALS PRODUCE BIASED DATA

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[abstract] RATIONAL DECOMPRESSION TRIALS PRODUCE BIASED DATA

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Title: [abstract] RATIONAL DECOMPRESSION TRIALS PRODUCE BIASED DATA
Author: Survanshi, SS; Weathersby, PK
Abstract: Probabilistic mathematical models of DCS, which are fitted to calibration data using maximum likelihood, assume each individual dive is an independently random event. However, the data sources generally used are controlled research trials. Human trials, quite rationally, are truncated if earlier use of the test profile produces a sequence of DCS cases that are "unacceptable." Truncation can arise in simple testing of one profile, as well as in carefully designed sequential trials. Investigation the effect of sequential trial design by Monte Carlo simulations, we found that such trials can lead to statistical sampling bias resulting in overestimation of risk of DCS. Simple cases as well as a recent efficient trial design (Survanshi et al., UHM 24(Suppl): 22, 1997) are presented for illustration. The effect can be minor or it can be severe enough to increase hazard estimates by 50percent. For example, in the case of a dive trial planned to be truncated if 2 cases of DCS are observed within the first 9 dives or 3 cases are observed at any time within a total of 32 dives, an actual 5percent profile will appear, on average, to have a 7.1percent risk. Likewise, a 10 percent profile will produce, on average, a 15.9 percent incidence of DCS. This bias further confounds differences between laboratory data and real-life diving experience. (Supported by NMRDC work unit 63713N M0099.01A-1510)
Description: Undersea and Hyperbaric Medical Society, Inc. (http://www.uhms.org )
URI: http://archive.rubicon-foundation.org/680
Date: 1998

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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