Cross Sectional & Cohort Studies Flashcards

1
Q

observational studies

A

investigator observes study participants (does not assign exposure) and records exposure and outcome

investigator can NOT assign exposure but CAN select subjects accordingly

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2
Q

do observational studies use randomization

A

NO - randomization requires intervention (clinical trials only)

CAN do random selection of subjects from the population

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3
Q

types of observational studies

A
  1. cross sectional
  2. cohort
  3. case control
  4. clinical case series
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4
Q

cross sectional studies

A

study an entire population at a single point in time

sample: whole population OR random sample independent of exposure and disease

cases: prevalence NOT incidence because not evaluating over time

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5
Q

prospective cross sectional studies

A
  1. random group selected
  2. test for disease
  3. determine if they have exposure
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6
Q

retrospective cross sectional studies

A
  1. random group selected
  2. were they + or - for disease
  3. were they exposed
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7
Q

advantages of CS studies

A
  • generates hypothesis for clinical trials
  • quick, easy, low cost
  • can include more than 1 exposure and disease
  • represents an entire population
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8
Q

disadvantages of CS studies

A
  • temporality: can not confirm order of exposure and disease
  • causality: can not determine causality of exposure on disease because they are non-directional
  • survivor bias: only includes living subjects
  • misleading in short duration and chronic diseases
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9
Q

cohort studies

A

study a single cohort of subjects over time and record disease at it occurs

randomly selected subjects that all have something in common at enrollment

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10
Q

steps of cohort studies

A
  1. randomly select disease free subjects
  2. divide into exposed and not exposed
  3. follow each group and determine who develops disease
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11
Q

what analysis is made from cohort studies

A

disease incidence (risk) in exposed and unexposed subjects

if incidence is higher in exposed than unexposed, the exposure MAY be causal to outcome

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12
Q

are there confounders in observational studies

A

YES - can not ID every confounder because there is no randomization

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13
Q

prospective cohort studies

A

disease free subjects are divided into exposed and not exposed then followed over time to see if disease develops

can confirm temporality (exposure came before disease) because enrollment is disease free subjects

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14
Q

retrospective cohort studies

A

disease free subjects are ID’d from records then divided into exposed and not exposed

can NOT confirm temporality

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15
Q

advantages of cohort studies

A
  • best observational studies for COMMON diseases
  • works well with rare EXPOSURES only
  • no selection bias because all are disease negative at enrollment
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16
Q

disadvantages of cohort studies

A
  • does NOT work well for RARE diseases
  • can be costly or difficult if studying long term diseases
  • loss of follow up can be a problem
17
Q

what can be calculated from a cohort study

A

incidence proportion
incidence rate
hazard ratio
risk ratio
incidence rate ratio

18
Q

incidence proportion

A

risk of developing a disease in a population

newly diseased over time / entire population

19
Q

incidence rate

A

risk of developing a disease over a period of time

newly diseased over time / sum of days that individual subjects are at risk

20
Q

risk ratio

A

the ratio of disease incidence proportion in the exposed to that in the non exposed

21
Q

incidence rate ratio

A

the ratio of disease incidence rate in the exposed to that in the unexposed

22
Q

hazard ratio

A

the ratio of hazard of disease in exposed to that in the unexposed