Introduction
TRA / TPB is one of the most commonly used theories and has been applied to health behaviors for nearly 40 years. Thus, measurement of TRA / TPB constructs is well established.
This section will provide a brief introduction detailing common characteristics of TRA / TPB measurement, such as the types of scales used, the need for elicitation studies, and differences in direct and indirect measurement. Following the introduction, these characteristics of TRA / TPB measurement will be discussed in greater detail and specific to each construct.
- 5 or 7 point scales
- Bipolar or bidirectional scales (also known as semantic differential scales): unlikely / likely, disagree / agree, good / bad.
- Unipolar or unidirectional scales: very little control / complete control, not at all worried / extremely worried.
- Scoring from -3 to +3 such that:
- Belief that behavior will result in a positive outcome contributes positively to measure.
- Belief that behavior will result in negative outcome contributes negatively to measure.
- Elicitation studies: studies conducted to identify and select the content for the construct measures.
- Example: Before behavioral beliefs can be measured, the researcher must know what they are for the health behavior and population studied.
It is always important to pilot test your measures / instrument
- Direct measurement refers to measurement on a major construct (example: attitude, subjective norms, perceived behavioral control). These are usually more strongly associated with outcomes than indirect measures. Demonstrate these associations before proceeding to indirect measures.
- Indirect measurement refers to measurement on the minor constructs that comprise the major construct and then calculating these scores across the outcomes of the behavior.
- Example:
- major construct = attitude, indirect measurement measures
minor constructs = behavioral beliefs, evaluation of
behavioral outcomes; calculation discussed later
- It is important to show strong association between these measures and the major construct to ensure the appropriate beliefs were measured. If so demonstrated, these are of most interest.
- Assess instrument reliability by test-retest reliability and/or internal consistency reliability