CHAPTER 7

### KEY POINTS

• Effective critical care practice requires a rational approach to understanding, interpreting, and integrating clinical research studies, outcome measures, measures of association, and statistical testing relevant to research in intensive care units.

• Clinical research studies generally fall into one of two categories: observational studies or experimental studies, and each study type has different strengths and weaknesses.

• The goal of the observation is to evaluate associations between exposures and one or more outcomes of interest to investigators. The randomized controlled trial (RCT) is an important experimental design used to assess the efficacy of a medical intervention.

• Critical care research frequently relies on surrogate end points that allow demonstration of treatment effect with fewer patients over less time. Trials using surrogate end points should be interpreted with great caution.

• Appropriate interpretation of the results of treatment trials requires clear understanding of measures of association, including both relative risk and absolute and relative risk reduction (RRR). Making an educated decision about the application of a study's findings to one's patients also necessitates assessing the number needed to treat (NNT) to see a benefit to the population.

• Evaluating clinical research evidence also requires addressing the meaning of p values and confidence intervals. These statistical measures aid the assessment of whether observed differences in outcomes between groups reflect true differences or simply chance variation.

• To correctly interpret a variety of diagnostic tests, one must understand how well that test reflects the actual presence or absence of disease in any given patient. The sensitivity and specificity of a given test reflect how closely the result of that test reflects the “truth” about a patient's disease process.

• Qualitative methods can serve a variety of purposes in critical care research and should be reviewed no less critically than quantitative methods.

### INTRODUCTION

Without a rational approach to interpreting and applying research findings at the bedside, clinicians can be frustrated in their efforts to integrate the results of empirical studies into the care of their patients. Here we review important elements of clinical research study design, outcome measures, measures of association, and statistical testing relevant to research in intensive care units (ICUs). We also discuss the nature and role of qualitative research in intensive care medicine and summarize strategies to assess the rigor of a qualitative research study.

### STUDY DESIGN AND RELATED ISSUES

#### OBSERVATIONAL STUDIES

Clinical research studies generally fall into one of two categories: observational studies or experimental studies. Observational studies may include case series, case-control studies, prospective cohort studies, and cross-sectional studies. Each type of observational study has different strengths and weaknesses, but all involve observing the results of a subject's exposure to a factor of interest that was introduced independent of a research protocol. The goal of the observation is to evaluate associations between exposures and one or more outcomes of interest to investigators. Although observational studies can help identify associations ...

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