Week 2.1: Interventions Flashcards
What are the different forms of research investigating the effects of intervention?
- Case study/series
- Controlled trials
- Randomised trials
- Systematic review
What forms of bias are common in case series?
- Natural recovery
- Statistical regression
- Placebo effects
- Polite patients
What form of bias is most common in controlled studies?
Selection bias
What are some characteristics of a randomised trial?
- Groups are comparable at baseline
- Gives valid information about average effects of interventions
What is the main characteristic of a systematic reviews?
- Provide comprehensive transparent and minimally biased overviews of intervention effects (+/- meta-analysis)
Why do studies have inconsistent results?
- Bias
- Differences in types of patients included
- Differences in the way of treatment was administered
- Differences in the way the outcomes were measured
List the components of bias that can occur in intervention studies
- Natural recovery
- Measurement bias
- Statistical regression
- Polite patients
- Placebo/Hawthorne effects
- Attrition bias
- Recall bias
What is meant by natural recovery?
The condition resolves without intervention
What is meant by measurement bias?
Awareness of grouping may effect your measurement during the objective examination
What is meant by statistical regression?
Patients present for therapy when their condition is severe, so random reductions will likely lead to improvement
How can a polite patient cause bias?
Exaggeration of recovery when asked subjectively
What is attrition bias?
Withdrawal from the trial in a non-random way e.g. pessimistic patients more likely to drop out
What is recall bias?
Memory for extreme events and selective memories
What questions should be asked of a paper when critically appraising their methods?
- What are the features of a high quality RCT?
- Were treatment and control groups comparable?
- Was there allocation blinding of patients and assessors?
- Was there complete or near complete follow-up?
- Were the patients selected appropriately?
- Was the intervention applied appropriately?
- Was the comparison intervention appropriate?
- How many correctly guessed which intervention they received?
- Were the outcome measures appropriate?
- Do the patients in the study represent patients in the clinic?
What can the āpā value tell us?
If differences between groups are greater than would occur by chance alone
What does continuous measurement of effect size involve?
The amount of outcome is measure e.g. pain scale, gait speed, strength
What does dichotomous measurement of effect size involve?
Did the event happen i.e. yes or no
e.g. walking independently, recurrence of pain
What affects the width of a confidence interval?
- Sample size e.g. smaller = wider, larger = narrower
2. Variation in the population: measured by SD of sample?
What affects the width of a confidence interval?
- Sample size e.g. smaller = wider, larger = narrower
2. Variation in the population i.e. standard deviation
What three ways can reduction in risk produced by treatment be expressed?
- Absolute risk reduction (ARR)
- Number needed to treat (NNT)
- Relative risk reduction (RRR)
What is the 95% confidence interval?
It is the range within which we can be 95% certain that the true average effect of the intervention actually lies
What is the 95% confidence interval?
It is the range within which we can be 95% certain that the true average effect of the intervention actually lies
How is probability calculated?
Number of people with the condition/total number of people in sample
How is the risk ratio calculated?
Risk of event in intervention group/risk of event in control group
What is the risk ratio if the treatment has had no effect?
Risk ratio = 1
How are odds of an event calculated?
Probability of event happening: probability of event not happening
P: (1-P)
How is the odds ratio calculated?
Odds of event in treatment group/odds of event in control group
What is pre-test probability?
The prevalence of that factor in the general population
What is absolute risk reduction (ARR)?
the change in the risk of an outcome of a given treatment or activity in relation to a comparison treatment or activity. It is the inverse of the number needed to treat.
What is number needed to treat (NNT)?
The average number of patients who need to be treated to prevent one additional bad outcome (e.g. the number of patients that need to be treated for one of them to benefit compared with a control in a clinical trial).
What is relative risk reduction (RRR)?
It is a proportional measure estimating the size of the effect of a treatment compared with other interventions or no treatment at all. It is the proportion of bad outcomes in the intervention group divided by the proportion of bad outcomes in the control group.
