Acquiescence bias, also known as agreement bias, is a category of response bias common to survey research in which respondents have a tendency to select a positive response option or indicate a positive connotation disproportionately more frequently. Respondents do so without considering the content of the question or their 'true' preference. Acquiescence is sometimes referred to as "yea-saying" and is the tendency of a respondent to agree with a statement when in doubt. Questions affected by acquiescence bias take the following format: a stimulus in the form of a statement is presented, followed by 'agree/disagree,' 'yes/no' or 'true/false' response options. For example, a respondent might be presented with the statement "gardening makes me feel happy," and would then be expected to select either 'agree' or 'disagree.' Such question formats are favoured by both survey designers and respondents because they are straightforward to produce and respond to. The bias is particularly prevalent in the case of surveys or questionnaires that employ truisms as the stimuli, such as: "It is better to give than to receive" or "Never a lender nor a borrower be". Acquiescence bias can introduce systematic errors that affect the validity of research by confounding attitudes and behaviours with the general tendency to agree, which can result in misguided inference. Research suggests that the proportion of respondents who carry out this behaviour is between 10% and 20%.

A prominent psychological explanation attributes acquiescence bias to social norms that encourage agreeable behaviour. Evidence indicates that respondents approach surveys as though they are common conversations. A consequence of this is that the conventions that govern conversations influence the interpretation of survey questions and responses to them. Accordingly, pressure to conform to such norms and conventions prompts people to agree with stimulus statements. Based on research into the "Big Five" personality traits, individuals are predisposed to agreeable behaviour to differing degrees.

An explanation favoured by sociologists is that acquiescence bias is a product of the combination of the inclination to yield to the opinions of high authority individuals, and respondents' perception of the researcher/ interviewer as having higher authority. According to this explanation, when selecting answers, a tendency to agree with statements made by the interviewer arises from the respondent's intention of being polite or respectful. In support of this, there is evidence that indicates that respondents of lower social status acquiesce more frequently than respondents of higher social status. However, several studies have failed to replicate this finding.

Acquiescence bias is proposed to be a product of 'satisficing' behaviour. 'Satisficing' sees respondents select responses that are satisfactory or good enough, rather than engage in 'optimizing,' which produces best possible selection. This is done to conserve cognitive energy.

Roger Tourangeau, Lance J. Rips, Kenneth Rasinski have developed a cognitive model that proposes four stages to the process of survey response selection. Each stage entails several specific cognitive processes. For example, the Comprehension stage entails paying attention to a question or instruction set. They propose that some cognitive processes are required in order to select an answer whereas others serve as optional aids. A respondent's decision of which processes to employ from the model is determined by a number of influences, notably speed and precision.

The four stages:

Survey response effects can arise at any stage of the response process.

Two forms of 'satisficing' have been proposed: