the investigation of cause and effect Flashcards
What three types of studies come under observational study?
Cross-sectional studies
Case-control studies
Cohort studies
what is a cross sectional study?
try to determine the cause and effect when measuring exposure and disease at one point in time to for a hypothesis
What is a case control study?
investigate the cause and effect by comparing exposure in
- cases (with disease or outcome)
- controls (without disease or outcome)
usually retrieve
hypothesis generating or testing
What is a cohort study?
Cohort followed over a period of time
Investigate cause and effect by comparing outcome in :
- Exposed people
- Non - exposed people
usually prospective
- Looking forward in time over a log period
Hypothesis generating or testing
What is an experimental study?
2 types
- randomised controlled clinical trials
- non-randomised controlled clinical trials
researchers introduce an intervention and study effects
usually randomised, subject grouped by chance
explain randomised controlled clinical trials
gold standard
- ability to minimise bias obtained in information obtained from participants
random assignment of participants to experimental treatment or a control group (placebo)
patients kept unaware of which treatment received in trial, Known as blind study or single blinded
When would a non-randomised controlled clinical trial be used instead of a randomised one?
only used when random allocation is problematic
More prone to bias
explain a crossover design of a randomised controlled clinical trial
All participants enter both groups, in random order, often separated by a washout period in which they receive no treatment
Cancels many forms of bias as patients are exposed to all protocols
What is cause and effect?
a cause is anything that produces an effect or result
The knowledge of cause and effect relationship can lead to successful prevention strategies
What 3 steps can causation be summarised as?
- investigation of statistical association
- investigation of temporal relationships
- Elimination of alternative explanations
Explain the investigation of statistical association in terms of cause and effect
must first find an association between the risk and the disease
statistical association can be:
1. strength
2. consistency
3. specific
4. plausible
5. Dos-response relationship
Explain investigation of temporal relationships in terms of cause and effect
causal relationship depends on the temporal relationship
to show causation the suspected causal factor must have occurred before the effect or disease developing
Explain the elimination of alternative explanations in terms of cause and effect
need to show there is no other reason for the effect other than the causal factor
What is internal validity?
How well the study answers the clinical question for
the sample.
Measure and measurements.
What is External validity?
How well the study answer the clinical question for
the population.
Internal validity and accurate sampling
What are the sources of bias within study design?
Measurement bias
Recall bias
selection bias
systematic bias
explain measurement bias ang how it can be controlled
can occur during collection of baseline or follow up data
can be differential or non differential
can compromise internal or external validity
can be controlled by using the same instruments for all measurements and double blinding the study
What is a differential in terms of study bias?
miss classification
occurs when a measurement device leads to incomparable measurements between groups
What is recall bias?
can take many forms, may occur if people who have experienced an adverse event such as a disease, they are more likely to recall previous risk factors than those who have never experienced the event
compromises internal and external validity
What is selection bias and how is it controlled?
happens when participant chosen for the study influences the outcome of the study
also happens when participants are allowed to select the group they want to join
this can be controlled using randomisation sampling methods from the target population
name 4 more types of systematic bias
Performance bias
exclusion bias
detection bias
publication bias
What is performance bias?
refers to systematic differences in the care provided or in exposure to factors other than intervention of interest
What is exclusion bias?
Systematic differences in withdrawals from the trial
common reasons for exclusion of patients : ineligibility, protocol violation, early outcome, loss to follow up after study
What is detection bias?
Systematic differences in outcome assessment
cause an over or under estimate of the cause of the effect
Neyman bias (preferential detection of mild, slowly progressive cases of disease)
