Understanding How Individuals Make Travel and Location Decisions: Implications for Public Transportation (2008)

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34 Chapter 3 described background literature for the TPB. This chapter describes the TPB model itself. Guidance on the structure and use of the TPB can be found at Icek Aizen’s website (46). The TPB is illustrated in Figure 4-1. This model, which comes from the field of psychology, holds that human action is guided by three types of considerations: • Attitude toward the behavior (ATT)—refers to an individ- ual’s own evaluation of an action, such as riding transit. This is also called attitude. • Subjective norm (SN)—refers to an individual’s percep- tion of what others will think if he/she takes an action (e.g., what friends and parents will think if he/she rides transit). • Perceived behavioral control (PBC) or SCF—refers to an individual’s assessment of his/her own ability to take an ac- tion (e.g., his/her self-confidence in using transit). ATT, SN, and SCF all contribute to an individual’s intent to carry out a behavior. Whether an individual actually car- ries out the intent depends also on his or her SCF in carrying out the behavior. For each individual, these three considera- tions will have different importance or weighting depending on the behavior or action. For example, young teens, as com- pared with older adults, may be more influenced by the opin- ions of their peers in a decision to take transit. This research also focuses on two additional areas of input to the TPB model that the literature review shows to be rele- vant to residential choice and mode choice. These are (a) life- cycle stage and (b) the environment and services available. Life-cycle changes—leaving home for the first time, getting married, having children, having an empty nest, and so forth—will have a great impact on an individual’s attitudes about choice of residence. Life-cycle stage also can be expected to have an impact on an individual’s subjective norm (for example, “what my parents expect will influence when I have children”). The environment and services available will affect SCF (e.g., transit has to exist for me to be able to take it). Fig- ure 4-2 shows this extended model of the TPB. Direct measurement of the different constructs of the TPB can be done by asking respondents to provide ratings on a set of scales. The scales will vary depending on the behaviors being investigated. For example, intent can be measured by a set of scales such as the following: I intend to move to a compact neighborhood in the next 2 years. Strongly disagree: _1_:_2_:_3_:_4_:_5_:_6_:_7_: Strongly agree I will make an effort to move to a compact neighborhood in the next 2 years. Definitely false: _1_:_2_:_3_:_4_:_5_:_6_:_7_: Definitely true I plan to move to a compact neighborhood in the next 2 years. Extremely unlikely: _1_:_2_:_3_:_4_:_5_:_6_:_7_: Ex- tremely likely Attitude can be measured by a set of scales that should cap- ture both the experiential quality of a behavior and the judg- ment of the value of the behavior. For example, ATT can be measured by responses to the following statements: For me to move to a compact neighborhood in the next 2 years would be Extremely undesirable: _1_:_2_:_3_:_4_:_5_:_6_:_7_: Extremely desirable C H A P T E R 4 The Model of the Theory of Planned Behavior

For me to move to a compact neighborhood in the next 2 years would be Extremely unpleasant:_1_:_2_:_3_:_4_:_5_:_6_:_7_: Ex- tremely pleasant For me to move to a compact neighborhood in the next 2 years would be Boring:_1_:_2_:_3_:_4_:_5_:_6_:_7_: Interesting Subjective norm can be measured with a set of questions that not only measures what others think about a behavior, but also what others do themselves. For example, SN can be measured with the following: Most of the people who are important to me live in, or would like to live in, a compact neighborhood. Definitely false :_1_:_2_:_3_:_4_:_5_:_6_:_7_: Definitely true Most people whose opinions I value would approve of my moving to a compact neighborhood in the next 2 years. Definitely false : _1_:_2_:_3_:_4_:_5_:_6_:_7_: Definitely true It is expected of me that I move to a compact neighbor- hood in the next 2 years. Strongly disagree : _1_:_2_:_3_:_4_:_5_:_6_:_7_: Strongly agree Self-confidence can be measured with statements that reflect respondents’ confidence in themselves in performing an action. The statements can reflect the difficulty of per- formance or the likelihood that a respondent will be success- ful in performing a certain behavior. Other statements can reflect the degree to which the respondent has control over the situation in question. The following are examples of state- ments that may be used to measure SCF: Whether or not I move to a compact neighborhood in the next 2 years is completely up to me. Strongly disagree : _1_:_2_:_3_:_4_:_5_:_6_:_7_: Strongly agree I am confident that if I wanted to, I could move to a com- pact neighborhood in the next 2 years Definitely false : _1_:_2_:_3_:_4_:_5_:_6_:_7_: Definitely true For me to move to a compact neighborhood in the next 2 years would be Impossible : _1_:_2_:_3_:_4_:_5_:_6_:_7_: Possible In the fully specified TPB model, as explained by Aizen, each of the three psychological components (ATT, SN, and SCF) is potentially driven by a set of factors that may be thought of as a composite of belief and the relevance of the belief to the individual. Relevance means outcome evaluation when applied to ATT, motivation to comply when applied to SN, and power of control when applied to SCF. Each factor can be represented as the product of belief and its relevance. The sum of the factors represents indirect measures of ATT, SN, and SCF. The sum of the products of behavioral beliefs and outcome evaluations is an indirect measure of ATT. The behavioral be- lief represents an individual’s assessment of how likely an outcome is given a particular behavior. The outcome evalua- tion is the individual’s assessment of the desirability or un- desirability of this outcome. Typically these are measured on a seven-point scale. 35 Subjective Norm Attitude toward the Behavior Perceived Behavioral Control or Self-confidence B ehavior Intent Subjective Norm Attitude toward the Behavior Perceived Behavioral Control or Self-confidence B ehavior Intent Life Cycle (Age, Marriage, Children) The Environment and Services Available to Me (Urban Form, Transit, Auto Availability) Figure 4-1. The theory of planned behavior. Figure 4-2. The extended model of the TPB.

For example, if the behavior being considered is a move to a CN, then an example of a behavioral belief would be “If I move to a compact neighborhood, I will exercise by walking and bi- cycling.” This can be measured using a scale labeled disagree/ agree or unlikely/likely. An example of an outcome evaluation would be “For me, living in a neighborhood where I could exercise by walking and bicycling would be (undesirable/ desirable).” Moving to a compact neighborhood is the behav- ior, and exercising by walking and bicycling is the outcome. The sum of the products of normative beliefs and motiva- tion to comply is an indirect measure of SN. The normative belief represents the individual’s belief regarding some other person or group’s opinion of a particular behavior. The mo- tivation to comply is the degree to which the individual cares about that opinion. An example of a normative belief would be “My family thinks I should move to a compact neighborhood” (typically meas- ured using a scale ranging from “unlikely” to “likely”). An example of a motivation to comply would be the answer to the question, “How much do you care what your family thinks?” (measured on a scale ranging from “not at all” to “very much”). The sum of the products of control beliefs and power of control is an indirect measure of SCF. The control belief is an individual’s assessment of his/her ability to perform an action related to a particular behavior, whereas the power of control is the individual’s assessment of the importance of that com- ponent in allowing him/her to execute a behavior. An exam- ple of a control belief would be the answer to the question, “How likely is it that you could find an affordable home in a compact neighborhood?” The response would typically be measured on a scale labeled unlikely/likely. An example of a power of control would be “It would be easier for me to move to a compact neighborhood if I could find an affordable home there,” with the response typically measured on a scale labeled agree/disagree. Figure 4-3 shows the full TPB model. The TPB can be used in several ways to illuminate how individuals make decisions. First, it provides a framework for better understanding of the decision-making process, for example, examining how indi- viduals choose mode or residence depending on their atti- tudes, what they say others think, and their circumstances that can be expected to affect their SCF (e.g., how close they live to transit or how easy it is to walk). Second, the TPB provides a general model to explore a par- ticular decision (such as moving to a CN) by posing a set of rating questions to a group of respondents. That is, ask a large number of questions that might be related to a decision to move to a CN and then explore how the responses relate to ATT, SN, SCF, and intent. Third, the TPB provides a specific model that explicitly relates indirect measures of beliefs and indirect measures of the relevance of beliefs to direct measures of ATT, SN, and SCF. The research makes use of the TPB as a framework, as a gen- eral model, and as a specific model. 36 Behavioral Belief1 OE1 OEn MC1 MCn PC1 PCn Attitude toward the Behavior Perceived Behavioral Control or Self- confidence Intent B ehavior Subjective Norm X X X X X X OE: outcome evaluation MC: motivation to comply PC: power of control Behavioral Beliefn Normative Belief1 Normative Beliefn Control Belief1 Control Beliefn Figure 4-3. The fully specified theory of planned behavior.