Lecture 10/11 Cohort & Case control Studies, pretest Flashcards
T/F Matching is a process only utilized in Cohort studies and not Case-Control studies.
false both
T/F Using the standard 2 x 2 table commonly utilized in observational studies, it is the column totals that are know at the start of a Case-Control study
true
T/F It is possible to assign a study subject to the Case group by utilizing a poorly-sensitive assessment tool.
true
Which of the following Case-selection avenues are most commonly and appropriately utilized in Case-Control studies? Direct patient interview Scanning-electron microscope Validated questionnare A physician's medical diagnosis
A physician’s medical diagnosis
T/F Case-Control studies are designed in a way that study subjects are initially allocated to their respective group based on the presence of a known exposure.
False
What is a Case control study’s major flaw? Why?
So susceptible to Bias. in Criteria for diagnosis of disease, for eligibility to be in study, similarity of controls controls selected independent of exposure blinded of hypothesis and more
can case control studies calculate/yield incidence rates?
NO, only cohort can do incidence rates. CASE CONTROL STUDIES , already diseased. Can’t determined newly diseased if they already have it. Go back to your basics.
When cohort studies result in incident rates that are low values for both the exposed and non exposed, This is highly inconclusive, With these results, why would a case control study be MORE helpful?
CASE CONTROL STUDIES GIVE (OR’s) ODDS RATIOS. They start with diseased and look for exposure, therefore, telling us the ODDS of Getting the diseases, Vs a cohort that told us, whether exposed or not, you have a low chance incidence.. which really doesn’t help anyone, and OR’s of case control studies are better for this circumstance.
In a case Control Study, the Selection of controls must be (independent or dependent) of the exposure being investigated?
Independent, you are looking for exposure and you want your controls (non diseased) to all have random levels of Exposure. Otherwise if all of your non-diseased have high exposure, then your OR odds ration would be very low, and BIASED.
In Case control Studies, to see if there was bias in a study, you want to look where and ask what to questions?
Look at CONTROLS
ask:
1. are they representative of your cases?
2. Are they selected independent of exposure?
First ask, Where in this is he telling me how I allocated or divided people into groups. For the 3 analytical studies, What is each time and What are you looking for to determine the type?
- Interventional - randomized and force (control gets placebo)
- Case Control - know diseased (control is non diseased)
- Cohort - know exposed (control is non exposed)
For your Case control study, do you know columns or rows? Cohorts?
case control - columns - disease
cohorts - rows - exposure
Cohort - Case Control - Both
Things that describe or are good reasons to use above
1. if unethical 2. if limited resources 3. for Rare diseases 4. Want incidence rates 5. want odds ratio 6. if prospective 7. if retrospective 8. long latency 9. if multiple exposures
10. requires follow ups 11. multiple outcomes 12 represents temporality
Both = 1, 2, 7
Case Control = 3, 5, 8, 9 (note this is only retrospective)
Cohorts = 4, 6, 10, 11, 12
Cohort Retrospective = 3,8
Which of our 2 observational analytical studies is only retrospective?
Case control is only retrospective. If you have a disease, and your looking at exposure, doesn’t make sense to be looking into the future right?
What is known at the start of a Retrospective Study?
Both exposure and the outcome of interest have occurred.
What does temporality mean? Does prospective or retrospective better represent temporality? Which Type of study is then best for this?
Temporatlity, think linear progression, if this, then that, or B comes after A. If there are many confounders and you don’t have temporality, then this is not good, b/c you cannot make an determinations. Prospective studies, do not have wade through all the potential confounders, b/c you have more control over temporality and having good results. Cohort prospective studies represent temporality and because all case control studies are retrospective, they to not have temporality. This can lead to incorrect assumptions in retrospective studies.
The Mostdifficultpartofacase‐controlstudyiswhat?
controlselection
What are the DisadvantagesofRetrospective CohortStudies?
- lack of accesstocharts,databases,
records(maynot becomplete/thoroughenoughfor yourstudy) - “Information”maynotfactorinotherexposuresto
harmfulelements - Patientsmaynotbeavailableforinterviewifcontact
necessaryformissingorincompletedata - Exposure(orits“amount”)mayhavechangedover
time
What is the outcome of selecting similar controls?
Less confounders and less room for bias
For Cohort studies, when selecting the controls? in which order is best to worst for methods of selection?
A. Comparison Cohort B. General Population C internal
Internal is best
General population 2nd
Comparison cohort worst, means, select close as possible based on comparisons.
in Case control studies, why must cases be selected before your controls?
In matching your controls. you don’t want to match for anything that might be a risk factor.
3 types of Samplingofnon‐diseasedindividualsforNestedCase‐Controlstudies
o Survivor sampling (survivors)atendof studyperiod o Base sampling atstartof studyperiod o Risk Set sampling duringstudy periodatsametime whenCasewasdiagnosed
5 questions to ask of cohort studies?
- LTFU
- enough allotted time
- how was exposure defined & measured
- How was outcome defined & measured
- Confounders evaluated
IR’s are what? and the outcomes of what type of study?
Incident Rates are found in Cohort studies. Incidents of NEW DISEASE. meaning we were looking for disease, and KNEW exposure.
