Purpose of analytic studies
To test hypotheses regarding, for example:
- causes of disease
- methods for prevention of disease
- the effects of treatments
Concept of replication
- responses vary among people, replication allows us to seperate true effects from chance effects
What does a control group do
- provides context for evaluation the effect of interest
Without control gorup..
- dont know if anything else has changed in order to cause the change
Control group helps determine the cause of the decrease
Types of analytic studies
- experimental studies
- observational studies
Experimental studies outline
- researcher manipulates the conditions (intervenes in a natural process) and records the results
- aim is to control all other factors to isolate the effects of the intervention
- best wat to study causation
- randomisation can be used to ensure that effects of unmeasured factors are equalised across the intervention of control groups
Experimental studies are common throughout
Science
Observational all studies outline
- the investigator does not intervene, simply observes a naturally occurring process and collects information
- the idea is to get as close as possible to the information that would hav e been obtained if the experimental study could have been done
Example of experimental study
Example of an observational study
Another example of observational study
Types of experimental and observational analytic study designs
Experimental
- randomised control trial
Observational
- cohort study
- case-control study
What is the ‘gold standard’ analytic study
Randomised controlled trial (RCT)
Two important characteristics of RCT
- Randomisation (or random allocation) is used to create two comparable groups - one will have placebo treatment and other the experimental treatment. At the end any difference between the groups can be attributed to the difference in treatment.
- Control group - used to isolate the effects of the intervention
Blinding in RCT refers to..
…not knowing whether the participant is in the intervention or the control group
Several people may be blinded to the allocation including the participants, the people caring for patients, the people measuring outcomes, the lead researcher
Advantages of randomised controlled trial
- experiment - the best way to test an hypothesis
- if the trial is well conducted, differences in outcome can be attributed to the intervention
Disadvantages of randomised control trial
- may not be ethical or feasible
What is a cohort study?
Observational study, genereally carried out to test hypothesis
Characteristics of a cohort study
- participants are selected before disease has developed
- followed over time to determine development of disease
- information is collected about exposures at baseline and during follow-up
- cohort studies do have a control gorup, but allocation isn’t randomised there is always the potential for confounding
Advantages of cohort study
- closest observational study to randomised controlled trial
- good at emanining common outcomes
- can evaluate the effect of exposure on multiple outcomes
Disadvantages of cohort study
- long duration needed if the disease takes a long time to develop after exposure
- if the disease is rare, the number of participants needs to be very large
- it is very hard (if not impossible) to remove all the effects of confounding
What is a case control study
- observational study, genrellay carried out to test hypotheses
Characteristics of case- control study
- participants are chosen on the basis of their disease status: a group with disease (cases) and a group without (controls)
- information is collected form people with and without disease about exposures that occurred in the past (retrospective)
Case control study advantages
- relatively quick
- smaller then cohort studies, particularly for rare diseases
- can examine the effects of multiple exposures
