Participants may alter their behaviour because they know they are part of a study and this can lead to a lack of validity as the behaviour they exhibit is influenced by their interpretation of the research project and of the researcher and his or her behaviour towards them.
Demand characteristics; Cues in the way the researcher behaves and other features of the research situation which indicate the possible aim and/or hypothesis of the study to the participants, (that is, what the researcher expect will happen). Participants may or may not pick up on these cues; if they do they may alter their behaviour in order to comply with what they perceive to be the researcher’s expectations. However, occasionally participants may pick up on the cues and behave in the opposite way to what they think the researcher expects, (Hugh Coolican terms this the screw you effect!).
Participant reactivity, that is the extent to which Pps alter their behaviour in line with demand characteristics may be affected by dispositional traits within the individual participants relating to age, experience, identification with the researcher (e.g. gender, ethnicity etc), personality (e.g. traits such as agreeableness and conscientiousness)
Participant bias also includes factors such as social desirability and evaluation apprehension. Social desirability simply refers the idea that most people wish to behave in a socially desirable way in front of others and therefore if they know they are being watched their behaviour may differ to how it would be they did not have this knowledge. This is linked to evaluation apprehension, which again is fairly self-explanatory; many Pps are concerned about the judgement psychological researcher might make about them and therefore their behaviour may be affected by anxiety.
Overall, Pps’ behaviour within research studies is affected by top down processing, linked to the way in which they have actively interpreted the researcher’s interests and their research question.
Behaviour will also be affected by the rapport between the Pps and the researcher, i.e. whether or not the Pps identifies with him or her or not, (think about social categorization, ingroup/outgroup etc). How the participants interprets the research situation will affect the nature of the data they provide.
Participant reactivity and bias also links to other areas such as the credibility and trustworthiness of the data and where these are called into question due to a method being employed that is open to participant bias, the researchers may like to involve some form of triangulation in an attempt to overcome this.
Due to the need to informed consent in a study and the sharing of interview schedules for example before the data collection gets underway, participants may well have started to consider their views and how they might communicate them. This retelling of their stories for a new audience, (that is the researcher) may well alter the nature of that tale, however, qualitative researchers recognise that the data they collect is the product of the relationship between the researcher and the researched and will consider this in the reflexivity section of their report, considering, for example, how the data may have been altered had another researcher collected/analysed it.