Observational Studies (Sept 13) Flashcards
1
Q
Observational study design
A
- natural experiments
- investigator does not manipulate treatment or exposure to disease, but rather observes natural variation
- observe what exposures they choose and whether these exposures lead to disease
2
Q
Why use observational study design?
A
- some things are not ethical to tell people to do (can’t randomize someone to an experimental drug that is known to be harmful)
- can observe people who choose to smoke, etc. and study their disease outcomes
- usually applicable to the world
3
Q
Problems with observational studies
A
- prone to bias
- something about study design or population makes it difficult to be certain that what we saw was the truth
- eg: if you are doing a study on drinkers and lung cancer, you must know whether or not the participants are smokers (confounding)
4
Q
Case Report
A
- 1 patient
- unusual symptoms/syndrome
- don’t know cause
- first, describe and speculate about what might be causing the disease to occur
- can do lab tests, imaging, histology and describe what is happening
- describing how a person presents, what you did to treat, and what the outcomes are
5
Q
Why are case reports important?
A
- highlight unusual/novel findings
- bring new diseases to the attention of the medical community
- new side effects of drugs can be discovered
- identifying new genetic diseases that are very rare
- birth defects
- treatment failures
6
Q
Limitations of case reports
A
- case may not be generalizable (if it’s something that only strikes health sci students but then it strikes an eng student, we don’t necessarily know if this will apply)
- not systematic (if you have a unique case others might present differently and require different treatment)
- causes or associations may have different explanations (eg. someone may be stressed from an underlying heart condition and not because they don’t cry and process their feelings)
7
Q
Case series
A
- group or series of case reports
- involves patients with a specific presentation who were given similar treatment
8
Q
What is contained in a case series?
A
- detailed information about the patients (exposure pattern)
- demographic information
- diagnosis, treatment, response to treatment, and follow up after treatment
- defined protocol and inclusion/exclusion criteria (what type of people will be included in the study)
- try to pick up on typical cases (set definition and choose cases that fit that criteria)
9
Q
SARS case series example
A
- people who presented with SARS and another comorbid disease did worse than those without a comorbid disease
- this case study was important as when people first started coming in, it was unknown who would have a better outcome
10
Q
Why are case series important?
A
- same reasons as case reports but with more people
- can help identify or characterize rare conditions or treatment courses
11
Q
Why are case series limited?
A
- if the series is retrospective it will depend on the availability and accuracy of the data records (no control over how the data was collected)
- subject to selection bias because the clinician or researcher self selects the cases
- findings reported may not be generalizable
- it is often impossible to know what would have happened to the cases if they had not been treated
12
Q
Counterfactual
A
- if we could go back in time with people that we treated and not treat them, what do we think would have happened to them?
- take a group of people similar to them who got a disease but we didn’t treat them (control group)
13
Q
Case control studies
A
- control group gives context
- two groups of people and we compare what happens to them
- control group allows you to estimate what would have happened to the treated group had they not been treated
14
Q
Method for case control study
A
- define cases and recruit them into study
- every time a case joins the study, find someone who does not have the disease and recruit them into the study
- ask both participants the same questions about their exposure history
- compare exposure histories
- classify people as cases or controls and as exposed or not exposed
15
Q
How to select a case for a case control study
A
- if the interest is looking at the average patient, make sure you are not selecting the sickest patient so they are representative
- specify clear inclusion criteria of cases (DSM criteria, test score, etc.)
- incident cases preferable to prevalent (prevalent have often had disease for a long period of time and have survived- survivorship bias- tend to be not typical cases of that disease. Also can be hard to separate exposure from disease as if they’ve lived with it for a long time, they mgiht not remember if the disease came first or other unhealthy exposures were first)
