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.
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
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.
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.
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.
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
Table 83-1. Properties of Three Types of Data |Favorite Table|Download (.pdf)
Table 83-1. Properties of Three Types of Data
|Type||Numbers Are||Typical Level of Measurement and Properties|
|Quantitative||Amount or count||Cardinal|
|No frequency distribution|
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 ...