66 PART 2 Examining Tools and Processes

by intervention into treatment groups (in a parallel trial) or into treatment-

sequence groups (in a crossover design). Randomization provides several

advantages:»

» ^{It helps in reducing bias. It specifically helps to eliminate treatment bias, which}

is where certain treatments are preferentially given to certain participants.

A clinician may feel inclined to assign a drug with fewer side effects to healthier

participants, but if participants are randomized, then this bias goes away.

Another important bias reduced by randomization is confounding, where the

treatment groups differ with respect to some characteristic that influences

the outcome.»

» ^{Randomization makes it easier to interpret the results of statistical testing.»}

» ^{It facilitates blinding. Blinding (also called masking) refers to concealing the}

identity of the intervention from both participants and researchers. There

are two types of blinding:

• ^{Single-blinding: Where participants don’t know what intervention they’re}

receiving, but the researchers do.

• ^{Double-blinding: Where neither the participants nor the researchers know}

which participants are receiving which interventions.

• ^{Note: In all cases of blinding, for safety reasons, it is possible to unblind}

individual participants, as at least one of the members of the research

team has the authority to unblind.

Blinding eliminates bias resulting from the placebo effect, which is where

participants tend to respond favorably to any treatment (even a placebo),

especially when the efficacy variables are subjective, such as pain level.

Double-blinding also eliminates deliberate and subconscious bias in the

investigator’s evaluation of a participant’s condition.

The simplest kind of randomization involves assigning each newly enrolled

participant to a treatment group by the flip of a coin or a similar method. But

simple randomization may produce an unbalanced pattern, like the one shown in

Figure 5-1 for a small study of 12 participants and two treatments: Drug (D) and

Placebo (P).

FIGURE 5-1:

Simple

randomization.

© John Wiley & Sons, Inc.