Cohort and Case Control Studies- Krysiak

10Q on exam

Analytical Observational Studies evaluates the relationship between 2 or more variables and do or do not involve control groups?

do

Can observational studies claim cause and effect?

no!

• we are only aiming at quantifying an association between variables

• aka in analytical observational studies evaluating the “relationship” NOT CLAIMING CAUSE OR EFFECT bc this is OBSERVATIONAL

What questions can we answer with observational studies?

• measure effect of exposures

  • ex: tobacco smoke, unhealthy diet, illicit drug use, etc.

• we can add to our understanding of

  • adverse effects of meds, special populations (kids, pregnant, elderly), co-existing disease states, off-label uses

Do observational studies measure “the usual conditions” or “artificial conditions”? What are those conditions?

the usual conditions:

• a typical clinical setting

• interventions NOT ASSIGNED

• measures real world effects

(FYI: artificial conditions would be like in a lab, under watch and care)

What are incidence rates?

number of people w/ NEW diagnosis of disease/ number of ppl at risk

What are prevalence rates?

number of people with new AND existing disease/ number of ppl at risk

What are point prevalence rates?

number of people w/ new and existing disease/ number of people at risk AT A SPECIFIC POINT IN TIME

Review:

What are the main differences between the 3 types of rates?

incidence- think NEW people diagnosed

prevalence- NEW people+ Previously diagnosed people

point prevalence- like prevalence, EXCEPT it’s a specific point in time

Purpose of cohort study:

• presence/absence of the suspected causative factor “risk factor”

Purpose of case-control study:

• presence/absence of the suspected outcome “problem”

Is a cohort study prospective, retrospective, or both?

BOTH

Advantages and disadvantages of prospective cohort studies:

• advantages:

  • gather new data to answer research question

  • use reliable and validated techniques of measurement

  • clarify if the exposure occurred prior to outcome

• disadvantages:

  • expensive

  • time consuming

Advantages and disadvantages of retrospective cohort studies:

• advantages:

  • quickly find results

• disadvantages:

  • limited to studying things only available in the data

  • errors and omissions of factors

Is a case-control study prospective, retrospective, or both?

RETROSPECTIVE ONLY

Example of Cohort study:

FYI

• basically were comparing a group exposed to a risk factor (smoking) to those not

• we follow them overtime, and see if the outcome we believe develops (ex: lung cancer)

Example of case-control study:

FYI

• we take a group that has an outcome (diabetics) to those who don’t (non-diabetics)

• we retrospectively look at their histories and draw conclusions from those risk factors

  • ex: we look at all the diabetics history and see they ate candy for every meal versus the control group who ate a balanced diet all their life… we could conclude that maybe the risk factor of eating candy for every meal leads to diabetes…

    • remember CANNOT SAY IT CAUSED THE DIABETES THO

Relative risk is used for __________ studies. Odds Ratio is used for ______________ studies.

relative risk: cohort studies

odds ratio: case-control studies

How do you calculate relative risk?

• risk exposed / risk unexposed

  • RR= [a/(a+b)] / [c/(c+d)]

    • WILL GIVE U EQUATION

    • YOU JUST HAVE TO KNOW WHERE ON THE TABLE TO FILL IN

• RR> 1 means exposure increases risk of outcome

• RR< 1 means exposure decreases risk of outcome

How do you calculate odds ratio?

• odds of exposure among cases compared to odds of exposure among controls

• Odds ratio= (a/c)/ (b/d) OR (AD)/(BC)

  • WILL GIVE EQUATION

Advantages of cohort and case-control studies in general:

What is the difference between a population- based and nested case-control study?

• population-based: conducted within a defined base pop

• nested: conducted within a cohort study

What are the 3 types of bias?

1. confounding

2. selection

3. recall

Explain the 3 types of bias:

• confounding

  • variable other than exposure of interest that affects the outcome

• selection

  • difference between treatment and control groups resulting from the way they were selected

• recall bias

  • ppl may remember things differently than how they occurred

Data sources can be either primary or secondary. Explain each:

Primary: newly gathered for research

• like questionnaire, interview, etc.

Secondary: collected for another purpose

• like medical claims databases, electronic medical records

Helpful table I made for review of cohort/case-control studies:

	Cohort	Case-control
presence/ absence of:	risk factor	outcome
type of perspective	both- pro and retro	only RETRO
good for studying rare:	exposures	outcomes
calculating	relative risk	odds ratio
do we have controls?	yes	yes