Observational Studies

Question 1

What are observational studies?

Answer 1

observe the effect of an exposure (or intervention) on an outcome without “interfering with anything
looks for association, not causation

Question 2

Why are observational studies performed?

Answer 2

often more:
-practical
-feasible
-real world (wider inclusion criteria, real-life situations)

Question 3

What is the challenge with observational studies? What are the 3 major threats to observational studies?

Answer 3

is the association real or due to something else? (is there internal validity?)
3 major threats: bias, confounding, chance

Question 4

What are the types of observational studies?

Answer 4

case reports/case series
cross-sectional
case-control
cohort

Question 5

Describe case reports.

Answer 5

describes and interprets an individual case
usually written as a narrative
-no predefined methods or outcomes
patient described in detail
observations described in detail
-exposure and outcome(s)

Question 6

What do case reports often describe?

Answer 6

unexpected events
unexpected adverse effects
important variations of known diseases
weird observations that cant be explained by known disease

Question 7

What are the advantages of case reports?

Answer 7

useful in identifying new or unusual trends or diseases
useful in identifying new drug effects (good or bad)
describe novel interventions:
-treatment
-diagnostic procedures
suggest areas for further research

Question 8

What are disadvantages of case reports?

Answer 8

difficult to interpret
-spontaneous appearance and disappearance of signs/symptoms
-placebo effect
-other influences
cant confirm or prove anything

Question 9

What is a case series?

Answer 9

collection of individual reports which typically occur within a fairly short period of time
can be hypothesis forming or world altering

Question 10

What are cross-sectional studies?

Answer 10

looks at population or study sample at one point in time
-snapshot of what is happening at that time

Question 11

What kind of information do cross-sectional studies collect? How do they collect information?

Answer 11

collect info on:
-exposure
-outcome
-health status
-health behaviours
collect information by:
-surveys/questionnaires
-chart reviews
-administrative data

Question 12

What are cross-sectional studies useful for? What can they not determine?

Answer 12

describing prevalence
-proportion of a population or sample that has a condition
CANT determine incidence
-number of new cases with condition over a specific time
can be analytical (looking for associations)
-factors that might be associated with one another
-cant determine if an exposure causes the outcome

Question 13

What are the advantages of cross-sectional studies?

Answer 13

good for determining prevalence
useful for quick examination of potential associations (hypothesis generating)
inexpensive

Question 14

What are the disadvantages of cross-sectional studies?

Answer 14

limited to what we know about the potential associations
-did the exposure precede the outcome?
-other contributing factors?
-transient effects

Question 15

What are case-control studies?

Answer 15

retrospective (looking back in time)
compare 2 groups
-cases=ppl with the outcome
-controls=people without the outcome
-compare the proportion of cases with the exposure to the proportion of controls with the exposure
try to have the cases and controls as similar as possible except for the outcome

Question 16

Describe the importance of case selection for case-control studies.

Answer 16

need to be very specific about the outcome
-want a validated outcome
ideally incident (new) cases over prevalent cases
-prevalent cases: dont know when the outcome occurred and if the exposure preceded it
-incident cases: we know when the outcome occurred and can be sure the exposure preceded it

Question 17

Describe the importance of control selection for case-control studies.

Answer 17

want the exposed and unexposed groups to be as similar as possible
-should come from same population as cases
often use multiple controls for each case
-increase sample size…decrease random error
-increases the power of the study
-eg 4:1=4 controls for every case

Question 18

How are cases and controls matched in case-control studies?

Answer 18

often use matching to help ensure groups are similar
-helps decrease confounding
-can only match on factors we know (sex, age, location, baseline cholesterol, etc)

Question 19

What are the advantages of case-control studies?

Answer 19

good for studying rare diseases or outcomes
relatively quick to do since the outcome has already occurred
good for establishing association (leads to further research)

Question 20

What are the disadvantages of case-control studies?

Answer 20

not randomized-susceptible to confounding
susceptible to bias
only suggests associations-cant prove cause and effect

Question 21

What are cohort studies?

Answer 21

groups (or cohorts) of subjects are created and compared according to exposures
-exposed vs unexposed group
-groups followed over time to see if outcome occurs
similar to an RCT but we didnt randomize subjects into groups or assign the exposure

Question 22

What is the best type of observational study for finding a valid association?

Answer 22

cohort study

Question 23

What are the two types of cohort studies?

Answer 23

prospective
-conducted in real-time
-have control over what data you want to collect and where its coming from
-at the start, outcome hasnt occurred yet
retrospective
-good for long follow-up studies (observation is already complete)
-use retrospective data collected prospectively
-data limitations

Question 24

What type of exposure can be studied in a cohort study?

Answer 24

any type of exposure
-drug
-procedure
-occupational
-environmental

Question 25

True or false: exposure and outcome do not have to be clearly defined for cohort studies

Answer 25

false
must be clearly defined and exposure must precede the outcome

Question 26

Describe the importance of cohort selection for cohort studies.

Answer 26

groups should be as similar as possible
select from same population
can have more than one comparator group

Question 27

What are the advantages of a cohort study?

Answer 27

provide highest level of evidence for observational studies
can study multiple outcomes after a single exposure

Question 28

What are the disadvantages of a cohort study?

Answer 28

susceptible to bias
not randomized so susceptible to confounding
more resource intensive than other observational studies