Study Design and Sampling

Question 1

Descriptive studies

Answer 1

Describe characteristics of disease in the population without identifying associations or causal inferences

Question 2

Observational studies

Answer 2

investigation of associations or causal inferences that are occurring in the population without manipulation or intervention from the researcher

Question 3

Experimental Studies

Answer 3

Researcher intervenes to allocate individuals to treatment or control groups then measures the effect

Question 4

3 types of observational studies

Answer 4

1. cross-sectional
2. cohort
3. case-control

Question 5

Cross-sectional study

Answer 5

analyzes data across as population at a single point in time using prevalence – sampling is representative of the population NOT based on exposure or outcome

a “snapshot”

Question 6

Cross-sectional studies identify ____ NOT ____

Answer 6

cross-sectional studies identify association NOT causation

Question 7

What is a critical aspect of cross-sectional studies?

Answer 7

which animals you select to sample (needs to represent target population)

Question 7

Why is questionnaire data collection difficult to do well?

Answer 7

always introduces bias (lies, mistakes, etc.)

Question 8

Advantages of cross-sectional studies

Answer 8

1. relatively easy, quick, and inexpensive
2. can study multiple exposures/diseases/outcomes
3. no loss to follow up
4. no case or control selection bias
5. used to ID high groups

Question 9

Limitations of cross-sectional studies

Answer 9

1. not useful in establishing causal relationships
2. prevalence can underestiamte disease risk if the sick die, recover quickly, or are removed
3. impractical for rare disease
4. relies on good sampling

Question 10

Case-Control Studies

Answer 10

studies that start with selecting cases and controls, then look back to ID exposures (sampling is based on outcome)

Question 11

Case-control study design (5)

Answer 11

1. define hypotheses
2. develop case definition
3. develop control definition
4. access and select cases and controls
5. conduct study, analyze data, report results

Question 12

How should controls be selected for case-control studies?

Answer 12

• should be similar to cases but without disease
• should have the opportunity for exposure and diagnosis

Question 13

Controls in a case-control study provide the _____

Answer 13

estimate of exposure rate among non-diseased

Question 14

What calculated value is used in case-control studies?

Answer 14

odds ratio (how many times greater are the odds of disease among exposed than among non-exposed)

this value will estimate relative risk

Question 15

Why can’t you calculate incidence rates?

Answer 15

you started with identification of prevalent cases

Question 16

Advantages of case-control studies (3)

Answer 16

1. best for rare diseases
2. inexpensive and fast
3. can study several potential exposures at the same time

Question 16

Limitations of case-control studies (5)

Answer 16

1. control group hard to pick
2. high potential for bias
3. can’t calculate incidence, prevalence, relative risk, or attributable risk
4. can’t assess rare exposures
5. problems with temporal sequence of data

Question 17

Cohort Study

Answer 17

selection of exposed vs. unexposed groups, then comparing the incidence of disease among them

Question 18

Advantages of cohort study (5)

Answer 18

1. controls bias
2. best assessment of exposure
3. can estimate multiple outcomes per exposure
4. more conclusive than case control studies
5. allows study of reare exposures

Question 19

What disease characteristics limit the use of cohort studies? (3)

Answer 19

diseases that:
1. have mild signs
2. do not require medical attention
3. can only be diagnosed with a medical visit

Question 20

Disadvantages of cohort studies (5)

Answer 20

1. not practical for rare disease
2. requires larger sample size
3. expensive
4. long time commitment for follow-up
5. can lose participants (causes bias, may reduce validity)

Question 21

Why do a clinical trial?

Answer 21

1. provide data for drug approval
2. compare treatments
   and more!

Question 22

What is the only factor that should differ among groups in a clinical trial?

Answer 22

treatment (all other factors should be the same)

Question 23

Different types of negative controls for clinical trials (3)

Answer 23

1. no treatment (hard to make this a “blind study”)
2. placebo
3. standard care (new treatment is added to standard in tx group)

Question 24

Types of random allocation

Answer 24

1. completely random
2. by pairs
3. within blocks

Question 25

Types of non-random allocation

Answer 25

1. systematic (gait splitting, every other animal, repeating tx order)
2. historical (borrowing information from animals enrolled as controls in previous studies)
3. clinicians disecretion (doctor decides)

Question 26

What is an important aspect of data collection to consider in a clinical trial?

Answer 26

masking/blinding procedures to keep those involved from knowing treatment assignments

Question 27

Advantages of clinical trials

Answer 27

1. high degree of internal validity
2. considered “gold standard” in medicine for establishing efficacy
3. required for drug approval
4. clinical trials minimize bias
5. assumption of causality (treatment cause whatever effect/outcome is present)

Question 28

Limitations of clinical trials (3)

Answer 28

1. ethics of placebos are under debate
2. expensive
3. can take a long time