6: intervention studies and group designs Flashcards
Main questions of psychotherapy research
Psychotherapy outcome research: see whether a treatment produces the desired and expected clinical results.
Psychotherapy process research: focus on the process of psychotherapy and its relationship with the outcome. Both qualitative and quantitative.
Psychotherapy outcome research
See whether a treatment produces the desired and expected clinical results.
Mostly qualitative approach is used.
Psychotherapy process research
Focus on the process of psychotherapy and its relationship with the outcome.
Both qualitative and quantitive methods are used.
James Lind
Did one of the first experiments with clinical trials in medicine on scurvy (disease caused by lack of vitamin C).
12 participants - 6 different conditions.
Only condition that worked: eating two oranges and a lemon a day.
BIASES:
- small sample
- no randomization of group
- experimenter may have had a secret favorite treatment.
Single-case study
Applying the intervention to a single participant and noting change
Strength/weakness of single-case study
S: simple; close to clinical practice
W: Sufficient only if changes in the absence of the intervention are known for certain.
Case series
A series of similar clients receive same intervention
Strength/weakness of case-series
S: sampling variability is reduced as sample size increase;
W: no explicit comparison with the absence of the intervention
Historical controls
Comparing a current cohort, to an earlier cohort before the intervention was available
Strength/wekness of historical controls
S: establishes and explicit comparison
W: services and characteristics of the population may have changed
Parallel control-matching
Choosing control subjects that are matched on known confounding factors
Strength/weakness of parallel control matching
S: rules out historical shifts
W: difficult to achieve balance; impossible to control for unknown confounders
Paralell controls randomization
One sample is divided randomly into different interventions
Strength/weaknesses of parallel controls randomization
S: can create balance on known and unknown confounders
W: clinicians who make decisions about inclusion will try to undermine random assignment
Parallel control randomization with allocation concealment
Randomization sequence is kept concealed from clinicans
Strength/weakness of parallel control randomization with allocation concealment
S: creates balance on known and unknown confounders, preventing subversion
W: clinicians may still attempt to guess the next assignment
Key design features in clinical trials
- Explicit inclusion and exclusion criteria (sampling)
- Control conditions
- Randomization
- Blinding or allocation concealment
- Outcome measures are standardized
Threats to internal validity in clinical trials
Selection bias Performance bias Detection bias Allegiance bias Attribution bias
Selection bias
Differences between test and control population regarding their structural compositions. –> randomization
Performance bias
Differences in the treatment apart from the intervention tested
happens when one group of subjects in an experiment (for example, a control group or an treatment group) gets more attention from investigators than another group.
Detection bias
Differences in observation of outcome parameter
Allegiance bias
A researchers belief in the superiority of a treatment can cause indirect systemic bias
Attribution bias
Related to differences in dropouts between test and control group
Threats to external validity
Process of consenting: patient who give their consent to participate have been proven to differ largely in severity of illness and other parameters to those who do not give their consent.
Consenting and selection criteria:
