To avoid attrition, applying some of these measures can help you reduce participant dropout by making it easy and appealing for participants to stay.
- Provide compensation (e.g., cash or gift cards) for attending every session
- Minimize the number of follow-ups as much as possible
- Make all follow-ups brief, flexible, and convenient for participants
- Send participants routine reminders to schedule follow-ups
- Recruit more participants than you need for your sample (oversample)
- Maintain detailed contact information so you can get in touch with participants even if they move
Attrition bias can skew your sample so that your final sample differs significantly from your original sample. Your sample is biased because some groups from your population are underrepresented.
With a biased final sample, you may not be able to generalize your findings to the original population that you sampled from, so your external validity is compromised.
Attrition bias is a threat to internal validity. In experiments, differential rates of attrition between treatment and control groups can skew results.
This bias can affect the relationship between your independent and dependent variables. It can make variables appear to be correlated when they are not, or vice versa.
Some attrition is normal and to be expected in research. However, the type of attrition is important because systematic bias can distort your findings. Attrition bias can lead to inaccurate results because it affects internal and/or external validity.
Attrition bias is the selective dropout of some participants who systematically differ from those who remain in the study.
Some groups of participants may leave because of bad experiences, unwanted side effects, or inadequate incentives for participation, among other reasons. Attrition is also called subject mortality, but it doesn’t always refer to participants dying!
Demand characteristics are aspects of experiments that may give away the research purpose to participants. Social desirability bias is when participants automatically try to respond in ways that make them seem likeable in a study, even if it means misrepresenting how they truly feel.
Participants may use demand characteristics to infer social norms or experimenter expectancies and act in socially desirable ways, so you should try to control for demand characteristics wherever possible.
You can control demand characteristics by taking a few precautions in your research design and materials.
Use these measures:
- Deception: Hide the purpose of the study from participants
- Between-groups design: Give each participant only one independent variable treatment
- Double-blind design: Conceal the assignment of groups from participants and yourself
- Implicit measures: Use indirect or hidden measurements for your variables
Demand characteristics are a type of extraneous variable that can affect the outcomes of the study. They can invalidate studies by providing an alternative explanation for the results.
These cues may nudge participants to consciously or unconsciously change their responses, and they pose a threat to both internal and external validity. You can’t be sure that your independent variable manipulation worked, or that your findings can be applied to other people or settings.
In research, demand characteristics are cues that might indicate the aim of a study to participants. These cues can lead to participants changing their behaviors or responses based on what they think the research is about.
Demand characteristics are common problems in psychology experiments and other social science studies because they can cause a bias in your research findings.
Using careful research design and sampling procedures can help you avoid sampling bias. Oversampling can be used to correct undercoverage bias.