PPHC 08 and 09: Evidence Evaluation (Epidemiology) – What are features of observational studies?

Question 1

What are the three types of epidemiology?

Answer 1

• descriptive (observational)
• analytic (observational)
• experimental

Question 2

What is the goal of descriptive epidemiology?

Answer 2

to examine patterns (of disease, health behaviours)

Question 3

What is the goal of analytic epidemiology?

Answer 3

to evaluate relationships between risk/protective factors and disease

Question 4

What is the goal of experimental epidemiology?

Answer 4

to evaluate effect of treatment/intervention on disease

Question 5

What are the 2 types of experimental studies?

Answer 5

• randomized controlled trial
• non-randomized

Question 6

What are the 2 types of observational studies?

Answer 6

• descriptive
• analytic

Question 7

What are the 3 types of descriptive observational studies?

Answer 7

• case report
• case series
• cross-sectional

Question 8

What are the 3 types of analytic observational studies?

Answer 8

• cross-sectional
• cohort
• case-control

Question 9

What are observational studies?

Answer 9

individuals are followed ‘observed’ in real-world settings

• no intervention/exposure assignment by researcher

Question 10

What is the goal of descriptive vs. analytic observational studies?

Answer 10

• descriptive: examine patterns (of exposure or outcome)
• analytic: evaluate relationship (between exposure and outcome)

Question 11

Do descriptive vs. analytic observational studies evaluate an intervention?

Answer 11

• descriptive: no
• analytic: yes – assigned by researcher

Question 12

Is there a hypothesis at the start of descriptive vs. analytic observational studies?

Answer 12

• descriptive: no hypothesis
• analytic: defined hypothesis

Question 13

Is there a hypothesis at the end of descriptive vs. analytic observational studies?

Answer 13

• descriptive: possible hypothesis
• analytic: confirm or reject hypothesis

Question 14

What are descriptive observational studies?

Answer 14

describe occurrence of an outcome (ie. disease)

• do not evaluate an intervention
• ‘hypothesis generating’ – no hypothesis at start, then possible hypothesis at end

Question 15

What are case reports?

Answer 15

detailed presentation of 1 case (n of 1)

Question 16

What do case reports do? (4)

Answer 16

• report a new or unique condition
• describe previously undescribed disease
• show unexpected new therapeutic effect
• report adverse events

(same as case series)

Question 17

What do case reports NOT do? (3)

Answer 17

• measure disease incidence (describe prevalent disease)
• identify risk factors
• identify cause of disease

(same as case series)

Question 18

What are case series?

Answer 18

detailed presentation of 2 or more cases

Question 19

What do case series do? (4)

Answer 19

• report a new or unique condition
• describe previously undescribed disease
• show unexpected new therapeutic effect
• report adverse events

(same as case reports)

Question 20

What do case series NOT do? (3)

Answer 20

• measure disease incidence (describe prevalent disease)
• identify risk factors
• identify cause of disease

(same as case series)

Question 21

What are cross-sectional studies?

Answer 21

observational study design that surveys exposures and/or outcomes at a single point in time (snapshot)

Question 22

What type of study are cross-sectional studies?

Answer 22

analytic – ie. measure association between exposure and disease

• evaluate association between exposure and outcome
• temporal sequence of exposure and outcome impossible to determine (don’t know which occurred first) – main limitation compared to cohort and case-control studies

descriptive – ie. focus on exposure or disease

• examines patterns (of disease, health behaviours)
• measures prevalence, not incidence

Question 23

What are analytic observational studies?

Answer 23

describe relationship between exposure and outcome

• disease can be the exposure or outcome
• can evaluate an intervention – though not assigned by researcher

Question 24

Analytic Observational Studies

What is the exposure?

Answer 24

• drug (ie. statin)
• intervention (ie. diet)
• policy (ie. drug plan coverage

Question 25

Analytic Observational Studies What is the outcome?

Answer 25

- clinical measure (ie. cholesterol) - disease outcome (ie. occurrence of cancer) - patient satisfaction

Question 26

What are key concepts for analytic epidemiologic studies?

Answer 26

- population: who we want to learn about - sample: who we will study

Question 27

Analytic Cross-Sectional Study What is an analytic cross-sectional study?

Answer 27

observational study design that surveys exposures and/or outcomes at a single point in time (snapshot)

Question 28

Analytic Cross-Sectional Study What are the 4 analyses?

Answer 28

- A: exposed, have outcome - B: exposed, no outcome - C: not exposed, have outcome - D: not exposed, no outcome

Question 29

Analytic Cross-Sectional Study Why can't you measure the risk of an outcome?

Answer 29

because we don’t know when outcome occurs - exposure and outcome are assessed at the same time in analytic cross-sectional study - therefore relevant concept is odds

Question 30

What is odds?

Answer 30

ratio of the number of ways the event can occur to the number of ways the event cannot occur odds = event / (1 - event)

Question 31

What is odds ratio?

Answer 31

measure of association odds ratio = (odds of outcome among exposed) / (odds of outcome among unexposed) = (a/b) / (c/d)

Question 32

What is OR > 1?

Answer 32

association - exposed group have higher odds of outcome compared to unexposed group - % increase = (OR - 1) x 100

Question 33

What is OR = 1?

Answer 33

no association

Question 34

What is OR < 1?

Answer 34

inverse association - exposed group have lower odds of outcome compared to unexposed group - % decrease = (1 - OR) x 100

Question 35

Cohort Study – Analytical Observational Study What is the starting point of a cohort study?

Answer 35

exposure

Question 36

Cohort Study – Analytical Observational Study What are the 3 steps of a cohort study?

Answer 36

- draw study sample from population - identify exposure status (exposed vs. not exposed) - follow individuals over time to see who develops outcome

Question 37

Cohort Study – Analytical Observational Study What is the key to cohort studies?

Answer 37

- outcome occurs after exposure - participants are followed up to that outcome(s) so researchers know when that outcome(s) occurred

Question 38

What is relative risk/risk ratio (RR)?

Answer 38

measure of association relative risk = (risk of outcome among exposed) / (risk of outcome among unexposed) = a/(a+b) / c/(c+d)

Question 39

What is RR > 1?

Answer 39

association - Exposed group have higher risk of outcome than unexposed group - % increase = (RR - 1) x 100

Question 40

What is RR = 1?

Answer 40

no association

Question 41

What is RR < 1?

Answer 41

inverse association - exposed group have lower risk of outcome than unexposed group - % decrease = (1 - RR) x 100

Question 43

Case-Control Study – Analytical Observational Study What is the starting point for case-control studies?

Answer 43

outcome (ie. disease)

Question 43

Case-Control Study – Analytical Observational Study What are the steps to case-control studies?

Answer 43

- identify cases (individuals with outcome or disease) - identify controls (individuals without the outcome or disease or interest) – note: cases and controls usually match on some factors or characteristics (ie. age, gender) - look at exposure histories

Question 44

Case-Control Study – Analytical Observational Study When might case-control studies be used?

Answer 44

when outcome (case) is rare

Question 45

Case-Control Study – Analytical Observational Study What measure of association does case-control studies use?

Answer 45

odds

Question 46

Case-Control Study – Analytical Observational Study Why is it important to analyze case-control studies?

Answer 46

cannot measure risk of an outcome because we don’t know when outcome occurs - case-control study design does not involve follow-up - in case-control study, one starts at the outcome - so relevant concept is odds

Question 47

What is the problem with mis-labelling 'case-control'?

Answer 47

‘case-control’ refers to design of the study, but is often confused with ‘cases’ and ‘controls’ which refer to participants in a study