CHAPTER 7 Having Designs on Study Design 91

Starting at the base: Expert opinion

At the base of the study design evidence pyramid shown Figure 7-2 is a descriptive

study design: expert opinion. When the condition of dementia was first identified,

few clinicians had seen patients with dementia. These clinicians served as experts

who would write about the dementia patients they treated and share their experi-

ences at medical conferences. This is what is meant by expert opinion, and while

it is helpful when conditions are first identified, expert opinion is considered a

very weak descriptive study design.

Making the case with case studies

Also at the base of Figure  7-2 are case studies and case series. To develop an

understanding of dementia when it was first identified, clinicians treating patients

needed to study them. They would write up case studies or case reports on individual

patients describing their symptoms and providing the best descriptive evidence as

possible. If the clinician was able to identify more than one patient, they could

write about a series of patients, which is known as a case series. While case studies

and case series are helpful for researchers when a condition is first identified, they

are considered as providing very weak evidence to use for causal inference.

FIGURE 7-2:

Levels

of evidence in

study designs.

© John Wiley & Sons, Inc.