Lecture 10/11 Cohort & Case control Studies, pretest

Question 1

T/F Matching is a process only utilized in Cohort studies and not Case-Control studies.

Answer 1

false both

Question 2

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

Answer 2

true

Question 3

T/F It is possible to assign a study subject to the Case group by utilizing a poorly-sensitive assessment tool.

Answer 3

true

Question 4

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

Answer 4

A physician’s medical diagnosis

Question 5

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.

Answer 5

False

Question 6

What is a Case control study’s major flaw? Why?

Answer 6

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

Question 7

can case control studies calculate/yield incidence rates?

Answer 7

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.

Question 8

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?

Answer 8

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.

Question 9

In a case Control Study, the Selection of controls must be (independent or dependent) of the exposure being investigated?

Answer 9

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.

Question 10

In Case control Studies, to see if there was bias in a study, you want to look where and ask what to questions?

Answer 10

Look at CONTROLS
ask:
1. are they representative of your cases?
2. Are they selected independent of exposure?

Question 11

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?

Answer 11

1. Interventional - randomized and force (control gets placebo)
2. Case Control - know diseased (control is non diseased)
3. Cohort - know exposed (control is non exposed)

Question 12

For your Case control study, do you know columns or rows? Cohorts?

Answer 12

case control - columns - disease

cohorts - rows - exposure

Question 13

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

Answer 13

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

Question 14

Which of our 2 observational analytical studies is only retrospective?

Answer 14

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?

Question 15

What is known at the start of a Retrospective Study?

Answer 15

Both exposure and the outcome of interest have occurred.

Question 16

What does temporality mean? Does prospective or retrospective better represent temporality? Which Type of study is then best for this?

Answer 16

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.

Question 17

The Mostdifficultpartofacase‐controlstudyiswhat?

Answer 17

controlselection

Question 18

What are the DisadvantagesofRetrospective CohortStudies?

Answer 18

1. lack of accesstocharts,databases,
   records(maynot becomplete/thoroughenoughfor yourstudy)
2. “Information”maynotfactorinotherexposuresto
   harmfulelements
3. Patientsmaynotbeavailableforinterviewifcontact
   necessaryformissingorincompletedata
4. Exposure(orits“amount”)mayhavechangedover
   time

Question 19

What is the outcome of selecting similar controls?

Answer 19

Less confounders and less room for bias

Question 20

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

Answer 20

Internal is best
General population 2nd
Comparison cohort worst, means, select close as possible based on comparisons.

Question 21

in Case control studies, why must cases be selected before your controls?

Answer 21

In matching your controls. you don’t want to match for anything that might be a risk factor.

Question 22

3 types of Samplingofnon‐diseasedindividualsforNestedCase‐Controlstudies

Answer 22

o Survivor sampling
(survivors)atendof studyperiod
o Base sampling
atstartof studyperiod
o Risk Set sampling
duringstudy periodatsametime whenCasewasdiagnosed

Question 23

5 questions to ask of cohort studies?

Answer 23

1. LTFU
2. enough allotted time
3. how was exposure defined & measured
4. How was outcome defined & measured
5. Confounders evaluated

Question 24

IR’s are what? and the outcomes of what type of study?

Answer 24

Incident Rates are found in Cohort studies. Incidents of NEW DISEASE. meaning we were looking for disease, and KNEW exposure.