Triad and the Theory of Reasoned Action/Theory of Planned Behavior



The Epidemiologic Triad is a traditional model of infectious diseases causation, as described previously it consists of an agent, host and environment. The Theory of Reasoned Action was developed by Martin Fishbein and by Icek Ajzen in the late 1960s. The Theory of Planned Behavior was developed from the Theory of Reasoned Action in 1985 (Hackman & Knowlden, 2014). We will be using the Triad to determine the host, agent, and environment while connecting it to the TRA and TPB.

The Theory of Reasoned Action is used to explain and predict behavior based on attitudes, norms and intentions. The construct of TRA are: behavioral beliefs, evaluations of behavioral outcomes which leads to attitude, then normative beliefs, motivation to comply which leads to subjective norms. Both the attitude and subjective norm lead to intention to perform the behavior, which results in the behavior. TRA does not account for people’s perception of the power they have over their behavior. That’s where the Theory of Planned Behavior introduces control beliefs, perceived power which leads to perceived control, then intention to perform the behavior, after which then the behavior occurs. The example that we will be using is the Ebola virus disease, a rare, communicable and deadly disease. It is transmitted through direct contact with body fluids, infected fruits or animals (CDC, 2018). In this case the agent is the virus, the host is the human, fruit, or animal, and the environment can be the community, local clinics, hospitals or a crowded house.

Behavioral belief produces in the host a favorable or unfavorable attitude towards a behavior. A male survivor of Ebola may want to engage in sexual activities but he is deciding on using a condom or not. Evaluation of behavioral belief are the values attached to the outcome or behavior, or the positive or negative judgment a host has. For example, an evaluation on whether or not to use condom. Attitude is a host’s disposition to act in a certain way. The host may decide not to use a condom because he has built immunity against the agent. Normative belief is when people close to the host agree or disagree over his behavior.

Motivation to comply is to agree with what the host’s friends and family thinks is the right behavior. I.e., using the condom to protect himself and others. Subjective norms are the host’s perception of social norms or what his peers’ beliefs are about the behavior. He may say that because the people that are important to him care about his actions, he wants to protect himself. Then, he may be willing to use condoms. External factors such as demographics variables, attitudes towards targets, personality traits, and other individual difference variables also play a role in behaviors.

As mentioned previously, TRA does not take into account for people’s perception of the control they have over their behaviors. This is where TPB comes in with control beliefs, beliefs about factors that facilitate or impede the performance of the host behavior. Perceived power are factors that facilitate or impede performance of the behavior. The host has the control over his behavior, what may facilitate him to engage in sexual behavior is his belief of being cured. Therefore, there is nothing to worry about. Perceived control is the individual’s control over their behavior. With perceived control the host is in control and can decide to perform the behavior.