1. CHAPTER 10 The participants: sampling and ethics
Research methods in clinical psychology: An introduction for students and practitioners Chris Barker, Nancy Pistrang, and Robert Elliott
CHAPTER 10
The participants: sampling and ethics

2. Participants
Sampling
Ethics

3. Sampling “Who?” Specifying and obtaining the sample Terminology
who will you be studying?
To whom can you apply the findings?
Specifying and obtaining the sample
quantitative and qualitative research
Terminology
“subjects”
alternatives: participants, respondents, “co-researchers”

4. Sampling/ ctd. Universe Target population Sample Intended sample
Achieved sample

5. Generalising the results
(Generalisability = external validity)
Sample population universe
bias, plausibility
error
Sample size doesn’t determine generalisability

6. Sampling in practice Specify the target population
Choose a sampling procedure
Determine the sample size

7. The target population Inclusion and exclusion criteria
Homogeneous sample (narrowly defined)
reduces extraneous variability
Heterogeneous sample (broadly defined)
better generalisability
Trade-off

8. Sampling procedures Goal: an unbiased sample Convenience sampling
every member of target population has equal chance of being selected
Convenience sampling
bias and under-representation of certain populations
Eliminating bias: not always feasible
gap between intended and achieved sample
estimating bias

9. Determining sample size
Statistical power analysis
depends on effect size, error rates
Statistical power of a study = likelihood of it detecting an effect that is actually present

10. Power analysis Four interrelated parameters: Sample size, N
Alpha (p-value in statistical tests): Type I error rate or false positive rate. Usually p<.05. The chance of a finding being wrong.
ctd./

11. Power analysis/ ctd.
Beta: Type II error rate or false negative rate (usually .20). The chance of missing something that is actually there
Statistical power = 1 minus Beta
Effect size: measures the strength of the relationship. Depends on the statistic used.
Cohen, J. (1992). A power primer. Psychological Bulletin, 112,

12. Alternative sampling approaches
Systematic replications
Falsificationist approach
look for counter examples
Popper
Snowballing/ networking
Purposive sampling
Theoretical sampling
grounded theory approach

13. Ethics: overview Central principles: Ethics review committees
Informed consent
Harms and benefits
Privacy and confidentiality
Ethics review committees
Professional obligations

14. Ethics: general issues
Ethics is a methodological issue
Procedural decisions have ethical implications
Ethical problems arise from viewing participants as objects
Ethical considerations require methodological trade-offs

15. Informed consent Full information Freedom of choice
Participants’ understanding needed
Competence to provide consent
Problems with deception
Freedom of choice
Voluntary decision (no coercion)

16. Informed consent form Description of the study
Explanation of its risks and benefits
Use everyday language (no jargon)
Offer to answer questions
“You can withdraw your consent at any time …”
Researcher’s and participant’s signature

17. Harms and benefits Minimisation of harm Direct harm: Indirect harm:
emotional distress, humiliation
Indirect harm:
withholding of benefit
Harm to participants v. benefits to humanity

18. Privacy and confidentiality
Privacy: right to not provide information to researcher
Confidentiality: right to withhold information from third parties
Protecting confidentiality:
anonymity
research codes
audio/videotapes
Limits to confidentiality

19. Cost-benefit analysis
risks versus benefits
greater risks of new procedures
benefits to participants versus benefits to others
greater potential risks require stronger safeguards

20. Ethics: conclusions Ethics review committees Professional obligations
to be familiar with code of conduct/ethical principles
to respond to participants who need professional services
Difficult choices: seek advice