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Technologies of Time |

Concepts of Time in Clinical Research

Jonathan M. Samet, MD, MS
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From Johns Hopkins University, Baltimore, Maryland.

Acknowledgments: The author thanks Alvaro Muñoz, PhD, for his helpful comments and insights.

Requests for Reprints: Jonathan M. Samet, MD, MS, Department of Epidemiology, School of Hygiene and Public Health, Johns Hopkins University, 615 North Wolfe Street, Suite 6041, Baltimore, MD 21205. For reprint orders in quantities exceeding 100, please contact the Reprints Coordinator; phone, 215-351-2657; e-mail, reprints@mail.acponline.org.

Ann Intern Med. 2000;132(1):37-44. doi:10.7326/0003-4819-132-1-200001040-00007
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Clinicians have an intuitive appreciation for the relevance of time to health and disease. Each day brings snapshots of individual patients: their current health and a profile of the factors that predict risk for disease. As these snapshots accumulate, the clinician is witness to the development of disease, the unfolding of natural history, and the consequences of interventions for prognosis. Patients invariably ask questions relating to time for which clinicians need answers: “How long until I am better?” “How long will I need this therapy?” “How long will I live?” Patients also want to know about their future risks for disease and whether these risks can be decreased. The time frames of reference for many questions may differ for patients and clinicians because patients seek answers to their immediate questions and clinicians maintain a long-term perspective.

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Figure 1.
Hypothetical etiologic exposure and phases of disease over time and age.
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Figure 2.
Age- and birth-cohort analysis of specific patterns of tuberculosis mortality rates in men in Massachusetts, 1880 to 1930(8).American Journal of Epidemiology

Reprinted with permission from the .

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Figure 3.
Survivorship lines of life tables for white men in three categories of tobacco use (19).Science

Reprinted with permission from .

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Figure 4.
Extended Kaplan-Meier curves, relative hazards, and relative times to AIDS from HIV seroconversion in calendar periods during which different types of antiretroviral therapy were used(52).

Adapted with permission from JAMA. 1998; 280:1497-503; copyright 1998, American Medical Association.

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