Anesthesiologists treat thousands of patients in their busy clinical careers; they also save thousands of lives. However, anesthesiologists also have a place in research where their work is far-reaching and affects untold millions of people worldwide. This chapter is dedicated to those anesthesiologists who actively undertake research and who keep abreast of the research literature in order to better serve their patients.

The chapter begins with some very basic principles of statistics that form the foundation for those methods most frequently used in regional anesthesia research. The basic principles, albeit more theoretical, are included in the hopes of offering more than a cookbook approach to the statistical procedures. Indeed, most statistical packages willingly “crunch data,” so I include only a limited number of calculations; preferring instead to emphasize appropriate application of methods and interpretation of results. It is hoped that this chapter will foster more effective dialogue between anesthesiologist and statistician. That is, by the end of the chapter, the reader should have a better understanding of what a statistician needs to know about studies and why this information is crucial to reaching valid research conclusions.

## What Is Statistics?

Sir Ronald A. Fisher (1890–1962), the father of statistics, considered the science of statistics to be mathematics applied to observational data: “Statistics may be regarded as (i) the study of populations, (ii) as the study of variation, (iii) as the study of methods of the reduction of data.”1 His definition has three important implications for research:

1. Investigators would like to apply their research findings to vast populations, but it is seldom feasible to study an entire population, so they must study samples from it.

2. Each sample studied will be slightly different, ie, there is variation among samples. Thus there will be differences among samples even from studies that have used the same design and methods.

3. Investigators summarize and test the data from their study sample in order to reach reasonable conclusions about the parent population that they can communicate to colleagues, journal editors, and to the public.

## Types of Data

The types of data collected in a study determine the type of statistical analyses. Table 83–1 describes the three types of data, what they represent, their typical level of measurement, and their properties.2

Table 83-1. Properties of Three Types of Data

Quantitative data are on a scale that has equal intervals, eg, the difference between 50 and 60 years of age is the same as the difference between 60 and 70 years of ...

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