Reactivity Definition

Medically reviewed by Dr. Jerry Crimmins, PsyD, LP
Updated February 22, 2024by BetterHelp Editorial Team

Have you ever caught yourself exhibiting the placebo effect psychology, acting differently when others can see you? Maybe you've noticed others behaving differently when they think no one is observing them. If so, you might have seen instances of a phenomenon psychologists call reactivity. This article provides a look at what reactivity is, different types of reactivity, its impact, and how you can develop healthy habits around it.

Reactivity definition

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Reactivity is a psychological phenomenon that happens when someone changes the way they behave because they know they're being observed. Their behavior might become more positive or negative, depending on the situation and the people involved. The person being observed may change their behavior based on their understanding of what the observer expects.

Types of reactivity

Beyond the basic definition, scientists have identified several distinct types of reactivity. The following are some special examples:

Hawthorne effect

The Hawthorne Effect happens during research studies when the people participating know they're being studied. The experimenters pay close attention to them, and they may change the way they behave as a result. This effect was named for the Hawthorne Works Plant, where researchers conducted a study on productivity. When an experimenter singled someone out and gave them attention, they worked harder and performed better.

John Henry effect

The John Henry Effect is a special case of the Hawthorne Effect. It also happens in research studies, but in this situation, the participants change their behavior because they know they're in the control group. They compare their behavior to what those in the experimental group are doing and how they’re reacting. Scientists see this as an attempt to overcome what the control group participants see as a disadvantage—that nothing interesting will happen in their group, and they will not receive special attention.

Experimenter effect

In a scientific experiment, the researchers must be careful not to let the participants know what they expect the study to show. If they do, the Experimenter Effect can happen. This is when the participants alter their behavior based on what they think the experimenter hypothesizes that they will do.

Observer-expectancy effect

The Observer-Expectancy Effect occurs when someone is perceived to give subtle cues as to what they expect. Regardless of whether they were intended or not, these cues influence the observer.

The concept derives from a study called the "Clever Hans" experiment. A philosopher and a psychologist wanted to find out if a certain horse (known as Clever Hans) could do arithmetic as its owner claimed it could. The owner would pose a question, and the horse would tap out the answers with its hoof.

The researchers noticed several things during their observations. First, if the owner didn't know the answer, the horse got the answer wrong most of the time. Second, if the horse couldn't see the owner, it couldn't get the answer right, either. Finally, they noticed that if the owner did know the answer, the owner's posture and facial expression changed as the horse's taps approached the correct number. The horse, then, was responding to what the owner expected of them.

Pygmalion effect and Golem effect


Reactivity can happen in a school setting, too. In the Pygmalion Effect, students change their behavior based on what they think the teachers expect from them. If a teacher expects the children to perform well, they perform better than they would if the teacher had no expectations.

The Golem Effect is similar to the Pygmalion Effect, except that it happens when teachers have low expectations of their students. When they do, the students tend to slack off more and show worse performance.

A similar thing can happen to teachers as well. If a student is more attentive to the teacher's lecture, the teacher tends to grade them higher even if their work isn't better than that of the students who didn't pay attention.

Both the Pygmalion and Golem effects can happen in other settings, too. In industrial settings, for example, a leader's expectations can change the way they treat employees. They give employees whom they expect to do better more time, attention, learning opportunities, trust, respect, and responsibilities. This can make it easier for those favored employees to perform better.

Bradley effect

The Bradley Effect is named after Los Angeles Mayor Tom Bradley, an African American candidate in the 1982 race for governor of California. Bradley was far ahead in the polls but failed to win. Experts have theorized that the reason for the discrepancy between the poll numbers and the election results was related to the voters' desire to give a socially acceptable answer.

Analysts have suggested that the Bradley Effect has happened in many other elections and is still a concern today.

The watching-eye effect

The Watching-Eye Effect is a type of reactivity in which people behave differently when they're being watched. People may change their behavior even when they merely see images of eyes, such as a picture of an eye posted on a wall. This effect may be useful for crime reduction because it gives people the sense that they're being watched even if no one is present. They know that they’re not real eyes, but they respond to them as if they were.

Why does reactivity matter?

Reactivity is a phenomenon that can have a great impact in many situations. Scientists, teachers, and leaders all need to be aware that reactivity can occur and take steps to overcome it. At the same time, law enforcement departments and others might make use of this effect to bring about positive results.

In scientific research

In scientific studies, researchers aim to design their experiments carefully to avoid unwanted reactivity. One option is to study people unobtrusively. To do that, researchers obtain information without the subjects even knowing that they are a part of a research study. For example, scientists might put up a poster in a public place and watch how people passing by react to it. To avoid reactivity, they would have to stay hidden or get their details from a hidden surveillance camera. Also, they would have to keep their study a secret until it was completed.

In research where unobtrusive observation is not possible, scientists often use a blind experiment design. In a blind experiment, information is withheld from subjects, technicians, details analysts, and those experimenting. This reduces the possibility of any kind of bias that might lead to reactivity. Often, the participants don't even know what hypothesis is being tested.

In a single-blind medical experiment, the subjects wouldn't know what treatment they were being given. For example, they wouldn't know whether they were getting a placebo or an actual medication.

In a double-blind experiment, the researchers and subjects are both unaware of who is in the control group and who is in the experimental group. For example, when testing a medication in a double-blind trial, neither researchers nor subjects know who is getting the placebo and who is getting the real medication.

In a triple-blind study, those monitoring the research are also unaware of who's in the control group. However, triple-blind studies are less common because, in many instances, the people monitoring the research need to be fully informed to ensure each participant is safe and receives ethical treatment.


In education, teachers might benefit from understanding that the way they respond to their students may be influenced by reactivity. They might aim to avoid basing their evaluations of students on factors other than their actual performance. If they recognize that their expectations of students can change the students' performance, they might choose to expect positive results whenever possible.


Getty/Vadym Pastukh
Explore reactivity and its effect in the world

In workplaces, leaders can use their understanding of reactivity to enhance the performance of workers. If they expect them to do well, give them attention, offer them learning opportunities, respect them, and lean toward trusting them more, the workers might be more likely to perform better.

What you can do if you're experiencing this

If you're in a situation where you or someone else is reacting strongly to something or someone, the consequences might be negative. For example, if you are a college student and your professor doesn’t expect the best of you, you may have trouble making the grade you desire. If you're a worker and your boss doesn't give you the opportunities you want, it may be because of their reactivity. As a parent, you may be puzzled at your child's bad behavior, not realizing that you're treating one of your children differently based on your expectations.

If you believe instances of reactivity—initiated either by yourself or by others—are having negative consequences on your life, you might want to consider getting in touch with an online therapist. Online therapy is readily available through online platforms like BetterHelp. Online therapy has repeatedly been shown to work as well as in-person therapy by many clinical studies

If patterns of reactivity are forming in your life, a licensed mental health professional is available to help you address your concerns. You may go through an online projective tests psychology to understand more about your personality. With BetterHelp, you can talk to a therapist completely online, and you have a reach to in-app messaging with your therapist in between sessions. Read what others have to say about their experience with BetterHelp below.

“It's been such a pleasure to impart and learn about myself and my behaviors to be able to understand what triggers me and why I allow things to affect me and how I react and respond to my surrounding. Dr. Fadil has been guiding me to better at allowing myself to listen to myself, to know when emotions and behaviors need to be faced and dealt with as an adult.”

“I've always been skeptical regarding feeling a sense of safety and understanding with a therapist. BetterHelp is new to me, though Victor has been nothing but understanding and thoroughly honest. He puts me to work in the best way, though I, myself, am still learning to be committed -- his patience, sincerity and expertise forces me to truly reflect and take accountability for how I choose to think, feel, react and respond. I'm very happy with how our sessions have gone, and continue to look forward to them.”


If you have questions about reactivity and how it might be affecting you, you’re not alone. This is a common phenomenon that a licensed therapist can help you explore at your convenience. Reach out to get matched with an experienced therapist whenever you’re ready.
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