Study Design

Question 1

define descriptive studies

Answer 1

1. searches for patterns by examining characteristics of person, place, and time
2. one individual or group
3. includes case report or series and cross sectional studies

Question 2

define analytical studies

Answer 2

1. allows to test hypothesis on etiology or risk factors
2. 2 or more groups
3. includes cross sectional, case control, and cohort studies

Question 3

define interventional/experimental studies

Answer 3

1. investigate the efficacy of vaccines, therapeutics, interventions
2. 2 or more groups

Question 4

describe case control studies

Answer 4

1. 2 or more groups
2. retrospective
3. investigate risk factors (exposure) using surveys or looking back into available data
   -outcome assessment simultaneously at enrollment
4. control group must be chosen appropriately using specific inclusion and exclusion criteria
5. use ODDS RATIO to express association of factor with disease
   -CANNOT calculate relative risk because we artificially created our population
6. pros: quick, low cost, helpful for rare disease
7. cons: unknown time sequence, survivor and recall bias
8. subjects selected based on OUTCOME status, so cannot calculate prevalence or risk ratio!

-CAN calculate: odds ratio
-canNOT calculate: prevalence, incidence, risk ratio

Question 5

describe cohort studies

Answer 5

1. 2 or more groups
2. compare exposed and unexposed
   -both groups are susceptible to the risk of getting the outcome/disease
   -evaluates one risk factor and multiple outcomes
3. control group must be chosen carefully
4. can be prospective or retrospective
   -can calculate incidence
5. outcome assessed prospectively, exposure assessed simultaneously at enrollment
6. can calculate odds ratio AND relative risk!!
7. pros:
   -less recall bias
   -primary data source
   -can study multiple outcomes of one exposure = good for rare exposure
8. cons: long time frame, higher cost
9. subjects selected on exposure status
   -used when interval between outcome and exposure are reasonable
   -can’t definitely establish causality
   -study incidence and causes!

-CAN calculate: RR, OR, prevalence, incidence (all the things!)

Question 6

describe cross sectional studies

Answer 6

1. used to study PREVALENCE at one point of time
2. outcome and exposure assessed simultaneously at enrollment
3. can calculate prevalence, risk ratio, and odds ratio
4. pros:
   -can study multiple exposures/outcomes
   -time invariant exposures
   -short time frame
   -low cost (if exposure and outcome not rare)
   -easy to conduct
   -no ethical difficulties
5. cons:
   -unknown time sequence: don’t know if exposure preceded outcome
   -cohort effect
   -not useful for rare exposures/outcomes
   -survivor and recall bias: secondary data
   -does NOT assess incidence
6. is a snapshot in time
   -longitudinal study: multiple studies over time; may sample different individuals in the same population
   -sampling without regard to exposure or outcome/disease status; subjects simply chosen from an available population
7. useful for establishing preliminary evidence in a future advanced study

Question 7

describe case reports/series

Answer 7

descriptive data; quantitative or qualitative

report: in depth study of a specific animal or group of animals

series: grouping of similar studies

pros:
-help to ID new trends or diseases, use hypotheses to test
-can dive deep into a rare or emerging disease
-can be published quickly and lead to the start of a structured investigation
-detect new drug side effects, novel therapy options

cons:
-can’t be generalized to the broad population
-researcher bias
-least reliable (evidence)
-causes and associations might have other explanations

Question 8

describe randomized control trials

Answer 8

1. randomized assignment of participants to experimental or control group
2. high level of evidence
3. control group receives placebo or an established standard treatment or vaccine
4. can be blinded
5. variables being studied should be the only differences between the experimental and the control groups
6. easier to control variable in a laboratory setting

Question 9

describe systematic review and meta analysis

Answer 9

1. exhaustive review of all relevant studies on a particular clinical or health-related topic/question
2. use of current literature/other sources (ongoing research, grey literature)
3. time consuming but cheap
4. studies investigating the same variables

Question 10

list the types of studies from most level of evidence to the least

Answer 10

1. Studies of studies (Systemic reviews, meta-analysis)
2. Intervention/experimental studies (Randomized controlled trial)
3. Analytical studies (Cohort studies, case-control studies)
4. Descriptive studies (Cross- sectional studies, case series, case reports)