THE THEORY OF PLANNED BEHAVIOR (TPB) was developed by Ajzen in 19851 to better understand and explain the variety of human behaviors. The TPB has been widely applied to examine and explain human behaviors in a broad spectrum of domains such as consumer behavior, recycling, technology adoption, and health behaviors.2–4 In the nursing context, the TPB has been employed to explain nursing actions such as hand hygiene,5 patient safety-related behaviors,6 use of filter needles,7 and use of clinical guidelines.8 In addition, the theory has been applied to patients with various diseases such as heart disease,9 cancer,10 diabetes,11 kidney disease,12 and mental disorders,13 as well as to individuals of all ages, including children10 and the elderly.11 Therefore, the TPB can be considered valuable for explaining and changing patient behaviors and nursing actions within the nursing domain.
With its various applications, the TPB has been evaluated and criticized by many researchers.14–19 Three major criticisms have been raised. First, researchers have stated that the TPB does not predict nonvolitional or spontaneous behaviors because it focuses only on deliberate and cognitive actions.14,15,18,19 Second, the TPB has been criticized for having low predictive validity.14,16,17 Among TPB-based studies, some have reported inconsistent relation- ships among concepts.9,16,17,20,21 Third, researchers have maintained that the TPB should include additional determinants for better prediction of intention and behavior.14,22 Although the theory's strengths and presumed limitations have been identified to a degree in many disciplines, the TPB has not been examined in depth based on a nursing framework for systematic theory analysis and evaluation. In one recent nursing study,15 the TPB was critically analyzed, but it was examined only briefly as one of several health behavior theories and without a critical framework. Considering the uniqueness of the nursing discipline23 and the TPB's frequent use in nursing science, it is necessary to analyze and evaluate the theory based on a comprehensive and detailed nursing framework in order to assess its value to nursing research. Moreover, given that the TPB was originally developed in 1985 and was last refined in 2012, there is a need to determine whether the theory can be effectively applied in the current nursing context, in which nursing care, human behavior, and related factors are continuously changing.
Statements of Significance
What is known or assumed to be true about this topic?
- The Theory of Planned Behavior has been broadly applied to explain and change various kinds of human behaviors in many domains, including the nursing context.
- The theory has been evaluated and criticized by many researchers, but it has not been examined in depth based on a critical nursing framework. Considering the uniqueness of the nursing discipline and the frequent use of the theory in nursing science, systematic analysis and evaluation of the theory are necessary based on a comprehensive framework designed for the nursing context.
What this article adds:
- The Theory of Planned Behavior was analyzed and evaluated on the basis of Fawcett and DeSanto- Madeya's framework for detailed and systematic assessment of nursing theories.
- The theory reflects the nursing metaparadigm concepts of human beings, environment, and health. The theory is also parsimonious and has both social and theoretical significance, testability, and empirical and pragmatic adequacy, but its internal consistency and clarity could be improved with use of consistent terms for theory concepts and propositions.
- Based on its successful application within the nursing context, the theory was found to be an effective tool for the development of knowledge in nursing research and practice. However, nursing researchers need to ensure that they accurately understand the terminology used for the theory's concepts and propositions in order to apply the TPB appropriately.
Therefore, the purpose of this article is to analyze and evaluate the TPB with Fawcett and DeSanto-Madeya's 2013 framework23 for detailed assessment of nursing theories. The TPB was developed in 19851 and refined in 1991,2 2005,24 2010,22 and 201225; this article was mainly based on the more recent 2010 and 2012 versions. The first part of this article is an analysis of the theory in terms of its scope, context, and content, and the second part is an evaluation of the theory with respect to its significance, internal consistency, parsimony, testability, empirical adequacy, and pragmatic adequacy. Finally, conclusions are presented regarding the applicability of the TPB for the ongoing development of nursing science and associated implications.
ANALYSIS OF THE TPB
According to Fawcett and DeSanto-Madeya,23 analysis of a theory should include detailed examination of its scope, context, and content based on what the author has written. These characteristics of the TPB are addressed below.
The first step in analyzing a theory is to identify its scope. Grand theories are relatively broad and general, and their concepts and propositions are more abstract than those of middle-range theories. Middle-range theories tend to be well defined and relatively specific, and their concepts and propositions are more concrete and limited in number.23 The TPB can be classified as a middle-range theory, as it consists of 5 concepts and 3 subconcepts that have concrete definitions and are interrelated within the domain of behavior prediction. In addition, middle-range theories are classified as descriptive, explanatory, or predictive in nature,23 and the TPB can be considered a middle-range explanatory and predictive theory. This is the case because it can explain relationships between concepts and predict the effects of concepts on intention or behavior in behavioral interventions.22,23
The second step in theory analysis deals with a theory's context. According to Fawcett and DeSanto-Madeya,23 this context consists of 5 parts: the nursing metaparadigm concepts and propositions addressed by the theory, the philosophical claims upon which it was grounded, the worldview reflected in the theory, the conceptual model used as its basis, and antecedent knowledge from nursing or other disciplines used for the theory's development. The TPB's context is discussed in these terms below.
Metaparadigm concepts and propositions
The nursing metaparadigm concepts consist of human beings, environment, health, and nursing, and the metaparadigm's propositions refer to 4 linkages between the concepts: human beings and health; health and environment; nursing and human beings; and human beings, health, and environment.23 Fawcett and DeSanto-Madeya23 asserted that the 4 nursing metaparadigm concepts and propositions reflect the unique characteristics of nursing.
In the TPB, human beings, environment, and health are all addressed. First, the TPB focuses on human beings in addressing various kinds of human behaviors and related factors; for example, Ajzen24(p117) assumed that “human beings usually behave in a sensible manner ... take account of available information and implicitly or explicitly consider the implications of their actions.” With respect to the environment, which consists of humans' personal relationships and all their surroundings, including the social, political, cultural, national, and global conditions affecting them,23 the TPB addresses social influence in terms of perceived norm, meaning “the perceived social pressure to perform (or not to perform) a given behavior”22(p124) or the “socially expected mode of conduct.”2(p199) Moreover, the theory's background factors (eg, culture, media, social networks), actual behavioral control, and perceived behavioral control (PBC) reflect the metaparadigm concept of environment.22 In the case of health, although this concept is not directly addressed in the TPB, the theory has been widely applied in health-related contexts such as smoking marijuana, drinking alcohol, and losing weight.2 Finally, nursing as a metaparadigm concept is not dealt with in the TPB because the theory was originally developed for the sociopsychologic discipline. Again, however, the TPB has been frequently employed in the nursing discipline.
As to nursing metaparadigm propositions, the TPB includes the continuous relationship between human beings and the environment. Ajzen22 stated that “people's behavior and various outcome indicators can vary greatly as a function of the social environment”(p244) and that “[individuals'] perceived behavioral control reflects both internal and external factors that may facilitate or impede performance of a given behavior.”(p171) In addition, as an environmental condition, perceived norm influences humans because it is one of “three determinants of [individual] intention [and action].”22(p322) All these statements indicate that the TPB reflects the interaction between human beings and the environment. However, even though the TPB includes the metaparadigm concepts of human beings, health, and environment, the relationships between human beings and health and between health and environment are not addressed in the theory.
Philosophical claims and worldview
Philosophical claims in nursing include ontological, epistemic, and ethical claims.23 Ontological philosophical claims pertain to the existence and the nature of the nursing metaparadigm, epistemic claims involve how knowledge or phenomena related to the metaparadigm came to be known, and ethical claims are related to the value system of people associated with nursing practice. Regarding the TPB, Ajzen22 did not explicitly state any philosophical claims in the theory. However, both ontological and epistemic claims are implied by the theory. From the ontological perspective, the basic entity in the TPB is human beings who can present different behaviors in the same situation, as humans can have various responses to a given phenomenon. As to epistemic philosophical claims, the TPB includes multiple factors that influence human behavior. The multifactorial process encompassed by the theory reflects the way that knowledge about the nursing metaparadigm is acquired.
Philosophical claims explain nursing values and beliefs and reflect a worldview of the relationship between human beings and the environment. Worldviews take 3 forms: reaction, reciprocal interaction, and simultaneous action.23 The TPB implies a reciprocal interaction worldview in which human beings have a mutual relationship with the environment as an integrated and holistic entity.
Conceptual model and antecedent knowledge
A conceptual model includes relatively abstract and general concepts and propositions that may be used to guide development of a theory.23 The TPB was derived largely from the Theory of Reasoned Action (TRA) developed by Fishbein and Ajzen in 1975.26,27 The TRA was designed to understand a behavior under volitional control, and it identified attitude toward a behavior and subjective norm (now perceived norm) as basic determinants of intention. This theory contained behavioral and normative beliefs, attitude, subjective norm, intention, and behavior, and was later expanded into the TPB with the addition of PBC.1 The PBC is based on Bandura's self-efficacy.28 Bandura asserted that people's behavior is influenced by their confidence in their ability to perform that behavior. This perceived self-efficacy is the PBC with respect to behavior included in the TPB.22
Regarding antecedent knowledge, the Expectancy-Value Model of Fishbein29 influenced the development of both the TRA and the TPB. For example, Ajzen1 derived the TPB's attitude from the Expectancy-Value Model. In this model, attitudes are formed by people's beliefs about and evaluation of the outcome of an action. Based on the model, Ajzen1,27 later developed normative and control beliefs for inclusion in the theory. As a result, the TPB contains 3 kinds of salient beliefs: behavioral beliefs influence attitudes toward a behavior, normative beliefs influence subjective norm, and control beliefs provide the basis for PBC.22
Examination of a theory's content constitutes the third step in theory analysis.23 Concepts, nonrelational propositions, and relational propositions are considered to be elements of a theory's content. Concepts are words or phrases used to describe a phenomenon, nonrelational propositions are constitutive definitions of concepts, and relational propositions present the relationship between 2 or more of a theory's concepts.
Concepts and propositions
The TPB concepts and propositions (both nonrelational and relational) are presented in Table 1, and the relationships among concepts are shown in the Figure. Background factors and the concept of actual behavioral control are included in the figure but not included in this critique because, according to Ajzen,22 background factors may not be related to the theory's other concepts, and actual behavioral control cannot be measured in reality and can be replaced with PBC. Regarding a relationship between PBC and behavior, PBC was originally shown as having a direct effect on behavior.2 However, in a later version of the TPB,22 Fishbein and Ajzen stated that PBC is more likely to moderate the effect of intention on behavior because having control implies that a person has the intention to perform a behavior. Therefore, the link between PBC and behavior is illustrated with dashed arrow in the Figure.24
Table 1. -
Concepts and Propositions of the Theory
of Planned Behaviora
||“A latent disposition or tendency to respond with some degree of favorableness or unfavorableness to a psychological object.”22(p70)
||“The more favorable people's attitudes and subjective norms, and the more they believe that they are capable of performing the behavior, the stronger should be their behavioral intentions.”25(p447)
“Perceived behavioral control is expected to moderate the relation between intentions and behavior such that intentions will predict behavior better when perceived control is high rather than low.”25(p449)
||“The perceived social pressure to perform (or not to perform) a given behavior.”22(p124)
|Perceived behavioral control
||“The extent to which people believe that they are capable of performing a given behavior, that they have control over its performance.”22(pp148,149)
||“Indications of a person's readiness to perform a behavior.”22(p34)
||“The stronger the intention, the more likely it is that the behavior will be carried out.”22(p17)
||“Observable events ... in a certain context and at a given point in time.”22(p24)
“A behavior as composed of four elements: the action performed, the target at which the action is directed, the context in which it is performed, and the time at which it is performed.”22(p24)
|“[Behavior's] proximal determinants: intentions and perceived behavioral control.”22(p66)
||“A person's subjective probability that performing a certain behavior will produce a particular outcome.”25(p440)
||“Behavioral beliefs produce a favorable or unfavorable attitude toward the behavior.”25(p448)
||“A person's subjective probability that a particular normative referent ... wants the person to perform a given behavior.”25(p441)
“Beliefs that important individuals or groups in their lives would approve or disapprove of their performing the behavior [Injunctive normative beliefs] as well as beliefs that these referents themselves perform or don't perform the behavior in question [Descriptive normative beliefs].”22(p16)
|“Normative beliefs result in perceived social pressure or subjective norm.”25(p448)
“If more important others are believed to approve than disapprove, and if the majority of important others perform the behavior, people are likely to perceive social pressure to engage in the behavior.”22(p16)
||“The subjective probabilities that particular factors that can facilitate or impede performance of the behavior will be present.”22(p214)
||“Control beliefs give rise to perceived behavioral control.”25(p448)
“If control beliefs identify more facilitating than inhibiting factors, perceived behavioral control should be high.”22(p17)
Adapted from Fishbein and Ajzen22
Used with permission.
EVALUATION OF THE TPB
From Fawcett and DeSanto-Madeya's perspective,23 a theory should be evaluated on the basis of 6 criteria: significance, internal consistency, parsimony, testability, empirical adequacy, and pragmatic adequacy. The evaluation can be performed on the basis of the results of analysis, previous critiques, and relevant research.23 The 6 criteria are applied to the TPB below.
The first step in theory evaluation is to examine a theory's significance in terms of social and theoretical significance. Social significance refers to the thoeory's importance to society, and theoretical significance is related to its contribution to the development of nursing knowledge. The significance of a theory should also be evaluated for its explicit inclusion of nursing metaparadigm concepts and propositions, philosophical claims, a conceptual model, and antecedent knowledge.23
As one of the most influential behavioral theories, the TPB has been widely used and has contributed to the prediction and alteration of various human behaviors. For example, this theory has been employed to explain significant personal and social actions such as illicit drug use, blood donation, consumer behavior, using public transportation, and conserving energy.3,25 Moreover, the TPB has been applied to influence health behaviors, including physical activity, dietary habits, drug use, sexual behavior, and screening behavior.4 Therefore, the TPB clearly has social significance. Regarding its theoretical significance, the TPB has contributed to knowledge development in nursing. Although the TPB is not a nursing theory, it can predict a number of health-related behaviors in the nursing context. Furthermore, Villarruel et al30 examined the applicability of the TPB to nursing situations by linking it to 2 conceptual models of nursing: Neuman's Systems Model and Orem's Self-Care Deficit Theory of Nursing. The authors found congruence between the TPB and the 2 nursing conceptual models, indicating that the theory can explain nursing phenomena and guide nursing research or practice. In other words, the TPB has theoretical significance with respect to its utility in nursing discipline.
Regarding the explicitness of the theory context, Ajzen22 did not address all the nursing metaparadigm concepts and propositions or explicitly present philosophical claims in the TPB. However, he did explicitly discuss its conceptual model and antecedent knowledge. Specifically, he explained that the TPB was based on the TRA and Bandura's Self-Efficacy Theory and that the TPB's attitude concept was derived from the Expectancy-Value Model. Although the TPB does not meet all of Fawcett and DeSanto-Madeya's expectations for a theory's significance, its social and theoretical contributions and its widespread application in nursing research and practice argue for its overall significance.
The second criterion of theory evaluation is internal consistency. To meet this criterion, first, a theory's context should be congruent with its content; second, a theory's concepts should reflect semantic clarity and consistency; and finally, a theory's propositions should exhibit structural consistency through clear linking of the concepts.23
The TPB's philosophical claims and conceptual model are congruent with its concepts and propositions. Although philosophical claims were not explicitly stated for the TPB, its concepts and propositions reflect a reciprocal interaction worldview and ontological and epistemic perspectives.22 For instance, the propositions describing relationships among background factors, beliefs, perceived norm, intention, and actual behavioral control expressed a mutual interaction between human beings and the environment. Also, change in human behavior was attributed to the TPB's subconcepts and concepts as multiple antecedent factors and could be predicted by these factors. In addition, the existence of human beings is a fundamental assumption of the theory, reflecting an ontological philosophical claim, and the TPB's various concepts and their propositions are the sources of learning about human behaviors, indicating an epistemic claim. With respect to a conceptual model for the TPB, its concepts and propositions are congruent with Bandura's Self-Efficacy Theory and Fishbein and Ajzen's TRA. For example, Ajzen's PBC is theoretically identical to Bandura's self-efficacy, and except for PBC, the TPB's concepts align with the TRA.22
Regarding the concepts' semantic clarity and consistency, these criteria were partially met. For the TPB, all concepts except for behavior were explicitly defined. Although no obvious definition was provided for the concept of behavior, Ajzen did state that a behavior must be defined in terms of its target, action, context, and time elements,22 indicating that the definition changes with the situation. However, the theorist did not use consistent terms for concepts. For example, Ajzen22,25 used the terms “performance,” “behavioral achievement,” and “action” interchangeably for behavior; “perceived social norms,” “perceived social pressure,” “perceived normative pressure,” and “subjective norm” for perceived norm; “perception of control” and “perceived control” for PBC; and “actual control” for actual behavioral control. The mixed use of these terms reduces the TPB's semantic consistency. Finally, the TPB's propositions reflect structural consistency because all linkages between concepts are clearly specified in the TPB. On the whole, the TPB partially meets the criterion of internal consistency.
The third criterion for theory evaluation is parsimony. A theory should explicate the phenomena of interest clearly and concisely with as few concepts and propositions as possible.23 Given its complexity, the TPB is parsimonious with 5 concepts and 3 subconcepts, their nonrelational propositions, and 8 relational propositions. These concepts and propositions serve to explain the TPB in clear and concise terms.
Under the criterion of testability, a theory should be evaluated in terms of whether its concepts are observable through use of instruments and whether its propositions are measurable through data analysis techniques. Empirical testability, an important aspect of a scientific theory's usefulness, can be established through a review of the research methodologies previously used to apply the theory.23 To evaluate the testability of the TPB, the search range for relevant studies had to be narrowed because the theory has been broadly tested for various human behaviors, and thus there is a massive amount of empirical literature available. For this study, the search was limited to the leading cause of death worldwide, cardiac disease.31 For cardiac patients, health behaviors such as physical activity, diet management, and smoking cessation are essential for their cardiovascular health and quality of life.32 Therefore, examination of the TPB's testability in this research area is suitable for assessing its larger usefulness in understanding and encouraging patients' health behavior.
Consequently, the search for relevant studies was conducted with the key words “theory of planned behavior,” “cardiac” or “heart,” “health behavior,” “lifestyle,” “physical activity,” “exercise,” “diet,” and “smoking” in 3 databases: PubMed, CINAHL, and Google Scholar. Under this critique's inclusion criteria, eligible studies (1) used the TPB as their conceptual or theoretical framework, (2) examined health behaviors in cardiac patients, and (3) were published in English from 1991 to 2020, as most of the theory's substance had been developed and empirically supported by 1991. Excluded articles (1) were review articles, theses, dissertations, or editorials, or (2) did not address specific TPB concepts in their methodology. After initial identification of 4301 studies, duplicates were eliminated, and the remaining studies were screened by checking their titles and abstracts. The full-text versions of 76 potentially useful studies were then reviewed, and studies were excluded if they did not measure TPB concepts or relationships even though they were guided by the TPB. Finally, 15 studies that addressed health behaviors in cardiac patients were selected for evaluation of the testability of the TPB (Supplemental Digital Content Table 2 available at https://links.lww.com/ANS/A34).
As shown in Supplemental Digital Content Table 2 (available at https://links.lww.com/ANS/A34), each major concept of the TPB was operationalized across the 15 studies. For instance, attitude, perceived norm, and PBC were, respectively, operationalized as attitude, perceived social norm, and perceived control with respect to exercise, cardiac rehabilitation (CR) program attendance, low-sodium diet, smoking cessation, and lifestyle change. Intention was operationalized as an intention to exercise, attend CR programs, change lifestyle, and quit smoking, and behavior was operationalized as physical activity, exercise adherence, CR program attendance, exercise stage transition, smoking cessation, and lifestyle change. However, most studies did not address all the major concepts, and therefore those studies were limited in their examination of relationships among concepts. Regarding the TPB's subconcepts, behavioral, normative, and control beliefs were, respectively, operationalized as beliefs about outcomes of exercise or stopping smoking, about other people's ideas regarding exercise or smoking cessation, and about factors that facilitate or impede exercise or smoking cessation. However, these belief subconcepts were assessed in only 4 of 15 studies. According to Fishbein and Ajzen,22 inclusion of belief subconcepts as basic factors can provide information on attitude, perceived norm, and PBC, but a given study's purpose and population should guide the decision about whether they are included.
The TPB concepts were shown to be observable through use of various instruments. Regarding behavior, exercise was mostly measured with the Leisure Score Index,9,20,21,33–36 and implementation of a low-sodium diet recommendation was measured with the Dietary Sodium Restriction Questionnaire,42,43 which was developed by Bentley et al45 based on the TPB. In addition, the Determinants of Adult Smoking Cessation instrument44 was developed to measure smoking cessation with the guidance of Ajzen and Fishbein.27 With respect to measurement of other TPB concepts, no single standard instrument has been developed that can be consistently applied to those concepts. Ajzen22 emphasized that each behavior must be defined in terms of its target, action, context, and time, and depending on the conditions surrounding a behavior, measurement of individual concepts may vary. In general, Ajzen stated that 3 to 6 items with 7-point scales can be formulated to measure attitude, perceived norm, PBC, and intention. For these concepts, 11 of 15 studies used 1- to 22-item questionnaires that differed depending on study purpose, and these scales were generally reliable with Cronbach α = 0.65 to 0.95. As to measurement of propositions through statistical procedures, correlation, regression, path analysis, and structural equation modeling were used in various studies. Relationships between concepts were mainly measured using correlation analysis, and influence of concepts on intention and behavior was identified using regression or path analysis.
As the fifth step of theory evaluation, the TPB's empirical adequacy was evaluated. To meet this criterion, theoretical assertions should be congruent with empirical evidence.23 A literature review of previous studies guided by the TPB was performed, and the findings of that review generally supported the TPB's assertions with some exceptions (Supplemental Digital Content Table 2 available at https://links.lww.com/ANS/A34).
One of the TPB's assertions is that attitude, perceived norm, and PBC influence intention. This assertion was generally supported by the empirical studies examined for this article. For example, in studies of exercise adherence or lifestyle change in cardiac patients,21,33,34,41 attitude, perceived norm, and PBC significantly contributed to intention to exercise during CR or to change lifestyle. However, in 5 other studies,20,38,40,42,44 1 or more of the predictors were not significant. For instance, attitude did not contribute to prediction of exercise intention,20 or neither attitude nor perceived norm explained intention,38 although other predictors significantly influenced intention. In 2 other studies,35,43 the significance of the predictors differed by time interval. These inconsistent relationships among concepts align with previous criticisms of the TPB. For example, some previous studies have found that attitude, perceived norm, and PBC played little or no role in intention.16,17,20 As a final point, some researchers9,36 did not examine attitude or perceived norm.
Another assertion of the TPB is that behavioral intention directly influences behavior. The findings of many studies were congruent with this assertion. For instance, intention explained exercise adherence, attendance of a CR program, and changes in exercise stages in various studies.33–35,37,39 However, some study findings did not support the assertion. In 3 studies,9,20,21 intention did not predict exercise behavior. Moreover, in a study of physical activity and CR attendance among patients with coronary heart disease,36 intention's predictive value differed by behavior: intention was a reliable independent predictor of CR attendance but not of physical activity.
The TPB also asserts that PBC moderates the effect of intention on behavior, but the studies reviewed did not examine the moderating effect of PBC. Ajzen22 mentioned that many researchers have investigated a direct effect of PBC on behavior because some previous studies had reported PBC's moderating effect to be nonsignificant or of little predictive value. Moreover, the TPB originally argued that PBC directly influences behavior. In this regard, only 4 of the 15 reviewed studies examined a direct effect of PBC on behavior9,20,21,36; among their results, PBC directly predicted exercise behavior or levels of physical activity. Finally, regarding the relationship between the 3 salient beliefs and 3 predictors, 2 studies34,44 reported that behavioral, normative, and control beliefs were related to attitude, perceived norm, and PBC. In conclusion, the TPB's assertions were generally congruent with study results for health behaviors among cardiac patients. The incongruent results can be attributed to the fact that the inclusion and contribution of concepts differed by study purpose, behavior, and population. Moreover, because researchers restricted themselves to the previous direct version of the relationship between PBC and behavior, PBC's possible role as a moderator requires further exploration and testing. Based on the limited number of studies reviewed, the TPB is considered to have acceptable empirical adequacy.
Pragmatic adequacy is the final criterion for theory evaluation. Assessment of pragmatic adequacy includes consideration of whether education and skill training are needed to apply a theory in nursing practice, its application in the real world, its feasibility for application, nurses' legal ability to implement and measure theory-based actions, its compatibility with expectations of the public and the health care system, and favorable outcomes of its application.23
First, Fawcett and DeSanto-Madeya23 stated that nurses need to have adequate education and special skill training to apply the theory in their practice. Because the TPB's concepts and propositions are parsimonious, it is expected that nurses can readily apply the theory in their practice. However, a full understanding of the TPB's content is necessary to apply the theory accurately. For example, without suitable education, it may be difficult for nurses to understand that the concept of perceived norm is perceived social pressure and that PBC can be used as a substitute for actual behavioral control. They may also be confused as to whether the subconcepts of beliefs and PBC's moderating effects should be considered because the TPB's concepts and propositions have evolved on the basis of Ajzen's evaluation of recent empirical evidence, as is reflected in his updated diagrams. Therefore, nurses need adequate education and training to be able to apply the theory concepts and propositions that best suit their practice and goals.
To meet the criterion of pragmatic adequacy, a theory should also be applied in the real world of nursing practice.23 In fact, the TPB has been applied to a large variety of patient behaviors—physical activity; risk-related, dietary, and screening behaviors; sexual behaviors such as condom use and other contraceptive behaviors; alcohol consumption; and smoking cessation.4 The disease populations examined using the theory have also varied and include patients with heart disease,9 cancer,10 diabetes,11 and kidney disease.12 Moreover, the TPB has been used to explain many nursing actions, including hand hygiene,5 patient safety-related behaviors,6 use of filter needles,7 and use of clinical guidelines.8 Thus, the TPB shows extensive real-world application in nursing practice.
The feasibility of a theory's implementation in practice should also be considered to determine its pragmatic adequacy.23 The TPB application requires relatively few human and material resources because its implementation is relatively uncomplicated, and its utilization for nursing actions does not require much time or money or complex procedures. In addition, because the TPB has been demonstrated to explain and predict human health behaviors, nurses are likely to be given financial resources to implement theory-based nursing actions. Therefore, the TPB is considered feasible for use in nursing practice.
Another question regarding a theory's pragmatic adequacy involves practitioners' legal ability to implement and measure a theory-based nursing action. Nurses have the legal ability to implement and evaluate TPB-based nursing actions. The theory has been widely accepted and used in multidisciplinary contexts, and no significant resistance in the form of financial barriers or professional doubt or distrust prevents its practical application for predicting human behaviors. All these points suggest that nurses' legal ability to apply the TPB in practice would be acknowledged by other health care providers.
A theory's compatibility with expectations for nursing practice should be considered in evaluating its pragmatic adequacy.23 The TPB is compatible with public and health care system expectations of nursing. For example, nurses can use this theory to predict and potentially change adverse health behaviors of patients with most kinds of health problems, and these actions are expected of nursing practice.
Finally, TPB-based nursing actions have been shown to produce favorable outcomes. As discussed previously, nurses have used TPB-based interventions to examine and improve health behaviors by identifying influencing factors and modifying patients' intentions in various circumstances. In summary, the TPB meets the criterion of pragmatic adequacy because the feasibility of its application in the real world of nursing actions has been demonstrated with positive outcomes and because it is compatible with expectations of nursing practice. Furthermore, the theory's application by nurses requires adequate education and skill training, and nurses have the legal ability to apply it in their practice.
IMPLICATIONS FOR NURSING
The TPB has contributed to the understanding and enhancement of human behaviors among various populations in broad nursing contexts. The theory's consideration of both personal and social influencing factors allows it to explain and predict many health-related behaviors in patients as well as their caregivers, family members, and nurses. In addition, the theory has guided development of behavioral interventions that have been shown to be effective in improving behaviors of patients and nurses alike. Furthermore, application of the TPB has contributed to evidence-based nursing practice by providing meaningful evidence for means of changing behaviors. Ajzen acknowledged that application of the TPB can differ according to its users' purposes, and nurses using the theory in practice should recognize the need to adjust its application according to the clinical context. Moreover, the TPB has been applied in many nursing interventions, but it cannot explain all human behaviors; many factors can influence these behaviors, and the concepts of the TPB may not capture this diversity. Therefore, while the TPB is useful in nursing research and practice, it should be considered as only one of several theoretical frameworks available to understand and modify human behaviors.
With respect to study limitations, we should acknowledge that the results of our evaluation of the TPB are based on the perspectives of the 2 authors and their collective interpretation of Fawcett and DeSanto-Madeya's framework. Moreover, our evaluation of the TPB's testability was confined to studies of cardiac patients' health behaviors. With these limitations in mind, we conclude that although the TPB is not a nursing theory, it has been successfully applied in nursing contexts with consideration of its linkages to conceptual models of nursing. Therefore, the TPB can be used by researchers and practitioners to explain and modify human behaviors in nursing research and practice.
The TPB was analyzed and evaluated on the basis of Fawcett and DeSanto-Madeya's framework for comprehensive assessment of theories applied in the nursing context. As a middle-range theory, the TPB addresses most concepts of the nursing metaparadigm and has both social and nursing significance. The theory shows partial internal consistency, having overall semantic clarity and consistency as well as structural consistency, and it is parsimonious in explaining and predicting human behaviors. In addition, the TPB is empirically testable with suitable instruments and data analysis techniques, and it can be broadly applied in nursing practice with meaningful outcomes. However, based on this critique of the TPB, the theory's internal consistency and clarity could be improved by using consistent terms for its concepts. Therefore, nursing researchers need to ensure that they accurately understand the terminology used for the theory's concepts and propositions in order to apply the TPB appropriately.
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