Susceptibility to influence: meaning and application

You want to decide which target group to approach first, and soon someone asks which group is easiest to persuade. Behind that question lies a scientific concept: susceptibility to influence. You will read where it comes from, why it is both a characteristic and a state and how to use it responsibly.

Susceptibility to influence is the degree to which people let their judgement or behaviour be influenced by others or by persuasive information.

Research describes it at two levels: as a personal characteristic that differs between people, and as a state that depends on the situation, such as involvement and the room to process information. In target group and communication research, the concept helps you determine which sources and which information carry weight for a group. It is not a fixed score for labelling individuals or predicting their behaviour.

The concept has no single originator. Several lines of research in social psychology and consumer research each developed one side of it.

Normative and informational influence. In 1955, Morton Deutsch and Harold Gerard studied variations of Asch's line-judgement experiment, in which participants judged in the presence of a group instructed by the experimenter, including face-to-face and anonymous conditions (Deutsch & Gerard, 1955). Their study distinguishes normative and informational social influence, a distinction that recurs in later research on susceptibility.

Susceptibility to interpersonal influence. In 1989, William Bearden, Richard Netemeyer and Jesse Teel developed a scale for consumer susceptibility to interpersonal influence, which they see as a general trait that varies across individuals. Their definition covers the need to enhance one's image in the eyes of significant others through products and brands, the willingness to conform to expectations in purchase decisions, and the tendency to learn about products by observing others or seeking information from them. Their studies supported a two-dimensional scale (Bearden, Netemeyer & Teel, 1989), which later researchers describe as normative influence (eight items) and informational influence (four items) (Modic, Anderson & Palomäki, 2018).

Susceptibility to persuasion techniques. Maurits Kaptein and colleagues developed the Susceptibility to Persuasion Scale (STPS) for sensitivity to individual social influence strategies. In a two-week intervention to reduce snacking, messages tailored to STPS scores led to a larger decrease than random or contra-tailored messages (Kaptein et al., 2012). David Modic, Ross Anderson and Jussi Palomäki built the Susceptibility to Persuasion–II scale (StP-II) with 54 items and ten subscales, including social influence, need for consistency and self-control. They tested the scale partly against responses to scam scenarios and state themselves that they cannot yet conclude that the scale works across different contexts (Modic, Anderson & Palomäki, 2018).

Susceptibility as a state. The elaboration likelihood model (ELM) of Richard Petty and John Cacioppo distinguishes a central route, in which people weigh arguments carefully, and a peripheral route, in which simpler cues such as the source carry more weight. In an experiment with 160 students, argument quality in an advertisement mattered more under high product involvement, and the celebrity status of the endorsers mattered more under low involvement. According to the authors, careful consideration requires both the motivation and the ability to process information (Petty, Cacioppo & Schumann, 1983; in more detail in Petty & Cacioppo, 1986).

Not passive recipients. The persuasion knowledge model of Marian Friestad and Peter Wright describes how people build knowledge about the goals and tactics of those trying to persuade them, and use that knowledge to cope with persuasion attempts (Friestad & Wright, 1994).

The scales mentioned treat susceptibility as a personal characteristic: people differ in how strongly others or persuasion techniques guide them. The ELM shows the other side. The same person may weigh arguments carefully when a topic is personally relevant, and rely on simpler cues when involvement, time or knowledge is lacking. A group may report following others' experiences, while this carries little weight in a specific choice.

Three questions make the concept usable. This is an editorial approach, not a validated model:

1. Which source of influence carries weight? Other people, the message content or simple cues such as the source.
2. How involved and how able is the group in this choice? Think of personal relevance, time and knowledge.
3. How does the group recognise and judge persuasion attempts?

Susceptibility is not readiness. Readiness segmentation groups people by how far along they are in their readiness to make a specific choice. Susceptibility concerns how strongly outside influence shifts their judgement. Someone can be very ready and hardly susceptible, or the other way round.

Susceptibility is not reactance. Psychological reactance, the response to a perceived threat to freedom of choice, will get its own article. With low susceptibility, influence shifts little; reactance can push someone in the opposite direction.

Susceptibility is not social norm perception. Social norm perception is what people think others do or approve of. Susceptibility is how much such a norm, or other influence, weighs in the judgement.

Susceptibility is not a technique. Cialdini's principles describe ways to exert influence; susceptibility describes the receiving side.

1. Describe the choice and the decision. Which choice does the target group make, and which decision do you want to support, such as the order of approach?
2. Reframe the question at group level. Do not ask who is easiest to persuade, but which sources of influence carry weight for this group in this choice.
3. Investigate sources and state. Ask open questions about what people pay attention to and whom they consult, and map involvement, knowledge and time pressure; see also How do you measure associations?. Only use an existing scale if it fits the population and purpose, and report its measurement properties.
4. Formulate hypotheses. For example: "in this group, other users' experiences weigh more than product specifications". Record what the hypothesis is based on.
5. Check the approach ethically. Does every group receive the same factual information? Is the sender recognisable? Are you avoiding choosing a group because it is less able to judge?
6. Test the messages. Compare variants on an outcome measure defined in advance; see From target group insights to testable messages.

This example is fictional and intended as an illustration.

Situation. A smart thermostat manufacturer is introducing a new model with budget for one campaign. The candidate groups are existing customers with an older model, recent home buyers and tenants.

Choice question. Which group does the manufacturer approach first, and with what information?

Available information. Customer service questions and a short survey among existing customers; little is known about the other groups. The marketing team wants to pick the group that is "most sensitive to what others do".

Suitable approach. The team reframes the question: which sources of influence carry weight per group, and how involved are people? A short study per group asks openly whom people consult (installer, neighbours, independent tests, landlord), what the trigger is, such as a renovation, and what they already know. The team calculates no individual scores and does not select on limited knowledge. Every group receives the same factual information on savings, costs and data processing; only the sender and level of detail may differ.

Possible interpretation. If new homeowners often mention the installer and are highly involved due to a renovation, a hypothesis is that detailed, verifiable information via installers suits them. If, for tenants, the decision partly lies with the landlord, that is not a matter of susceptibility but of decision latitude, and it changes the prioritisation.

Next step. Compare two variants in a limited trial on a predefined outcome measure, such as information requests. No results are known in this example.

Susceptibility touches on when influencing turns into manipulation. Testing the StP-II against scam scenarios shows that susceptibility can also mean vulnerability, and the tailored-message research shows that personalising to individual sensitivity is possible. The following boundaries are editorial advice:

• Make information clearer, do not bypass thinking. Use insights to make information fit better, not to discourage deliberation.
• Do not choose a group for its vulnerability. Do not select on limited knowledge, time pressure or financial vulnerability.
• Be transparent. Make sender and purpose recognisable. People judge persuasion attempts with their own knowledge of tactics; transparency respects that.
• Do not label individuals. Do not build personal susceptibility profiles without a clear legal basis, consent and necessity.

Read more in Neuromarketing ethics: key questions and responsibilities.

• Labelling people. "This customer is susceptible" is not a useful statement. Describe which influence carries weight in which choice.
• Reading self-report as behaviour. Scales measure what people report about themselves. That may differ from how they act in a specific situation.
• Ignoring context. Susceptibility changes with involvement, knowledge and time pressure; one measurement says little about another situation.
• Using group averages as individual predictions. A group average does not predict how one person responds.
• Transferring findings from another domain. The studies concerned snacking, scams and an advertisement shown to students. Check whether a finding fits your choice and population.
• Reading correlation as causation. A link between a scale score and behaviour does not show that the score causes the behaviour.

Susceptibility to influence describes how strongly others and persuasive information shape someone's judgement or behaviour. The concept has a characteristic side, which you describe with questionnaires, and a state side, which depends on involvement, knowledge and situation. Use it to see which sources and information carry weight for a group. Treat results as group-level hypotheses, test them in your own context and keep a clear ethical boundary: inform and persuade openly, without exploiting vulnerability.