Week 7 Flashcards by Sarah Drysdale

What type of studys is an analytic study

Ecological
Cross-sectional
Case-Control
Cohort

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Is case control and cohort studies observation or experimental

Observational

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What are 4 determinants we should consider when creating a cohort study

Those who enter the cohort study should be outcome-free
Selecting exposed and comparison groups
Following up participant
Determining outcome status

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Why is cohort study an observational study

There is no intervention you just follow up who gets a disease and who dosen’t

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Is the exposure determined before the outcome happens

Yes

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What are some disadvantages of cohort studies

More expensive
Time consuming
Not fesable for many disease

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What are some advantages of cohort studies

Better exposure and confounder data
Less vulnerable to information bias (recall bias can still happen)

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What is a prospective cohort study

You follow people for 10 years and compare incidence of disease

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What is retrospective study

You start at outcome and look back in time to see what caused the disease

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What are good ways to collect data for a retrospective study

Military data
Occupational study

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What are some advantages of retrospective study

Cheaper
Faster
Efficent with disease with long latenet period

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What are some disadvantages to a retrospective cohort study

Exposure and confounder data may be inadequate
More vulnerable to bias
Need an established recording system

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What is the incidence rate ratio

a/(a+b)/c/(c+d)

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if someone develops breast cancer but then latter dies what is there outcome

It is not death it is breast cancer

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What is the concept of person-time

People are in the study for a varied durations
Different times under exposure
Contribute differentialy to the study /.p09

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What are advantaged of Cohort studies

Valuable when exposure is rare
Can examine multiple effects of a single exposure
Easier to determine the temporal relationship between exposure and outcome
Allows measurement of incidence

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What are some disadvantages of cohort studies

Validity affected by losses to follow-up (selection bias)
Other factors may not be distributed evenly between exposure groups
Inefficient for evaluation of rare disease
Can be expensive and tine consuming
If retrospective they require good records

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What are limitations to cohort studies

May need large numbers of subjects to be followed for long periods
Loss to follow up to undermine validity
Not good for rare disease or those with long latency
Not good when exposure data are expensive to obtain

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You classify participants according to their outcome status

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Cases (+ disease)
Controls(no disease)
Then you need to ask for past exposures if the cases and controls were exposed or not exposed

Is a case-control population real

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No they are artifical

If we have a lot of people in a study should we reduce the size of the study

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Reducing the size of the study greatly reduces cost with a proper sampling we will get a correct value for the measure of association

What do you calculate when it is case control

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Odd provides provides the proper measure of association

What is the odd of exposure

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(A/C)/(B/D)

What is the caculation for the not-exposed group

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(A/B)/(C/D)

What are some qualifications for selecting cases

Very clear case definition requried Ideally case selection will invovle direct sampling of cases within a source population All people in the source population who develop the disease of interest will be included as cases If someone in the source population developed the disease of intrest would they

What is the definition of controls

A sample of the source population that produced the cases

What is the purpose of cases

To estimate the exposure distribution in source population that produced the cases

What are the two things that matter when selecting controls

1. Controls must come from the same source population as the cases 2. Controls must be selected independently of exposure

Where can you find controls

1. Population based controls 2. Nested controls from a cohort population/study 3. Hospital or clinic based controls 4. Family or friend control

What is the definition of population based controls

Controls selected from the general population most suitable when cases are from well-defined geographic area

What are sources of population-based control

Random digital dialing, cell phone or intrent subsurcibers residence lists, tax lists, voter registration, driver license holders

What is the advantage and the disadvantage of population based control

Controls often come from well-defined source population It is very time consuming harder to inspire participating may not recall past exposures as we as cases

What is the definition of nested controls

Controls selected from an existing cohort population

What is the advantage and disadvantage of nested controls

Controls come from clearly defined source population already enrolled willing participants Restricted to memebrs of existing cohort may limit the hypothes

What is the defention of Hospital or Clinic based controls

Controls selected from among patients at a hospital or clinic

What is the requirement of a hospital or clinic based control

Same source population as cases must consider the would criterion and the referral pattern illness should be unrelated to that is independent of the exposure under study 1. Illness that have the same catchment area as the cases 2. Illnesses that have no relation to the risk factors under study

What is the advantage of Hospital or clinic-based control

Easy to identify and access less time and money accuracy of exposure recall comparable to cases more willing to particpate These controls are not randomly selected this mean that hopsital based controls must be carefully selected to accurately represent the exposure history in source population

What is the defention of the matched design

The process of making a study group and a comparison group comparable with respect to extraneous factors

How can you account for confounding in matched design

Randomization in experimental studies Matching case to controls

How does matching work

For each case a control with the same characteristics will be selected

Whats the difference between individual matching and frequency matching

Indvidual matching is performed participant by participant and frequency matching providing similar distributions of confounder in groups

What is matching like in cohort studies

Exposed matched to unexposed Less common Expensive Sometimes unpractical May require control

What is matching in case control studies

After selection of a matching factor for each a case a control with the same characteristics will be selected A unit is not a person but a pair Paired anyalsis

What is the measure of association for cross sectional

Prevalence rate ratio

What is the measure of case control

Odds ratio

What is the measure of (Cohort)

Incidence ratio

Week 7 Flashcards

(46 cards)