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Types of Responses to PROM Items
Responses to a certain PROM item may vary between dichotomous and polytomous
scale of measurement. Some item responses are expressed as yes/no, present/absent,
and true/false. This is referred to as binary or dichotomous response scale of mea-
surement. However, many tests, questionnaires, and inventories in the behavioral
sciences include more than 2 response options. It is a set of answer choices that fall
into an order, e.g., from highest to lowest. For example, many personality question-
naires include self-relevant statements (e.g., “I enjoy having conversation with
friends”), and respondents are given 3 or more response options (e.g., strongly dis-
agree, disagree, neutral, agree, strongly agree). Such items are known as a polyto-
mous items, and they require IRT models that are different from those required by
binary items.
A scale may be composed of pictures, numbers, or categories [ 2 ]. Recording of
events is also one of the methods to determine the response that can be included by
the patient, e.g., diary maintain. The following types of response scales or options
may be used in a PRO instrument [ 3 ].
Types of Rating Scales
Likert Scale
The most frequently used rating scale is the Likert scale. Respondents are offered
the choice of selecting 1 of 7 pre-defined or even 9 pre-coded responses, with a
neutral point being equivocal along the continuum of the scale. Likert scales may
evaluate:
• Agreement (strongly agree, agree, undecided, disagree, strongly disagree),
• Frequency (very frequently, frequently, occasionally, rarely, never),
• Importance (very important, important, moderately important, of little impor-
tance, unimportant),
• Likelihood (almost always true, usually true, occasionally true, usually not true,
almost never true), or
• Other different attitudes (Fig. 2.1).
Fig. 2.1 Likert scale.
Example showing
agreement response
category options
M. El Gaafary