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138: Principles of Epidemiology and Research Design

Alex F. Manini; Kevin C. Osterhoudt

INTRODUCTION

Advances in medical toxicology are achieved through the scientific method using observations, derived from cases of poisoning and nonpoisoning due to xenobiotic exposures, to generate hypotheses. Subsequent research questions are analyzed with epidemiological investigation, and preliminary studies are examined with methodological scrutiny. Initial analytical techniques are improved, and confirmatory studies are performed. Ultimately, models relating cause to effect are formulated.

To optimize patient care, it is useful to grade the quality of available scientific evidence used to justify treatment recommendations. Decisions about how strongly to recommend a medical action will be based on the careful consideration of the risks of leaving a patient untreated, the potential benefits and harms of treatment, the quality of the guiding evidence, a balanced view of resource utilization, and the values of the person to be treated. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group has provided a framework for assessing and communicating levels of scientific evidence (Table 138–1).22 An understanding of basic principles of research design and epidemiology is required to interpret published studies and to lay the groundwork for future investigation in toxicology.

TABLE 138–1.GRADE System for Evaluating Clinical Recommendations
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TABLE 138–1. GRADE System for Evaluating Clinical Recommendations
Strength of Recommendation Quality of Evidence

Strong

Weak

High

Moderate

Low or very low
Strength/Quality Aggregate Implications
Strong/high

  • Recommendation can apply to most patients in most circumstances

  • Further research is unlikely to change our confidence in the estimate of effect
Strong/moderate

  • Recommendation can apply to most patients in most ­circumstances

  • Further research (if performed) is likely to have an important impact on our confidence in the estimate of effect and may change the estimate
Strong/low

  •  Recommendation may change when higher quality evidence becomes available

  •  Further research (if performed) is likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate
Weak/high

  •  The best action may differ depending on circumstances or patients or societal values

  •  Further research is unlikely to change our confidence in the estimate of effect
Weak/moderate • 

  • Other alternatives may be equally reasonable

  •  Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate
Weak/low

  •  Other alternatives may be equally reasonable

  •  Any estimate of effect, for at least one critical outcome, is very uncertain

EPIDEMIOLOGIC TECHNIQUES AVAILABLE TO INVESTIGATE CLINICAL PROBLEMS

Table 138–2 lists the different study formats discussed below.

TABLE 138–2.Epidemiologic Study Designs: Types, Measurements, and Advantages
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TABLE 138–2. Epidemiologic Study Designs: Types, Measurements, and Advantages
Study Designa Main Measurement Advantages
Clinical trial Efficacy Gold standard for drug development
Noninferiority trial Safety Noninferior drugs may be better tolerated, cheaper, or easier to use
Cohort Incidence, ...

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