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VET 414: Population Health > Clinicometrics > Flashcards

Clinicometrics Flashcards

1
Q

crude mortality

A

total # of deaths in a population / entire population

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2
Q

cause specific mortality

A

deaths from disease / entire population

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3
Q

case fatality mortality

A

deaths from disease / # of cases of disease

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4
Q

proportionate mortality for disease

A

deaths from disease / total # deaths in a population

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5
Q

prevalence

A

total number of cases in a population at a given time

cases at time T / population at time T

does NOT determine risk or probability of becoming a case

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6
Q

what type of study determines prevalence

A

cross sectional studies

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7
Q

can CS studies calculate risk/probability

A

no because it ignores disease duration

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8
Q

what factors influence prevalence

A
  1. population dynamics
  2. duration of disease

prevalence = incidence x disease duration

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9
Q

incidence

A

risk/probability of disease occurring in a time period

used to compare disease occurrence in one group versus another (exposed vs not exposed OR treatment vs controls)

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10
Q

what type of study determines incidence

A

clinical trials
cohort studies

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11
Q

what is required in order to calculate incidence

A

defined time interval (study length)

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12
Q

incidence proportion

A

new cases during study period / susceptible subjects

ranges from 0 to 1

assumes subjects do not have disease at the start of the time period and are not at risk of being removed from the population

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13
Q

limitations of calculating incidence proportion

A
  • diseases with recurrence
  • dynamic populations - requires calculation of incidence rate
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14
Q

incidence rate

A

new cases during study period / time that subjects are at risk of disease

denominator = sum of time at risk for all individuals in the population
- accounts for dynamic populations

measured in units of time (cases per X number of days)

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15
Q

2X2 tables - A, B, C, D

A

A: diseased + exposed
B: diseased + not exposed
C: healthy + exposed
D: healthy + not exposed

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16
Q

risk ratio (RR)

A

incidence proportion in exposed / incidence proportion in unexposed

relative risk, incidence proportion ratio

(# exposed new cases / total # exposed) / (# unexposed new cases / total # unexposed)
=
(A / A+C) / (B / B+D)

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17
Q

how do you interpret risk ratio

A

RR probability of developing disease in exposed vs unexposed

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18
Q

range of risk ratio

A

0 to infinity

RR > 1: exposure is a risk factor for disease
RR < 1: exposure is protective against disease

19
Q

risk difference

A

incidence proportion in exposed - incidence proportion in unexposed

(A/ A+C) = (B/ B+D)

absolute measure of risk
determines the importance of the disease

20
Q

interpretation of risk difference

A

for every (total # exposed), only X develop disease due to exposure

21
Q

incidence rate ratio

A

incidence rate in exposed/ incidence rate in unexposed

(# exposed new cases / time exposed are at risk) / (# unexposed new cases / time unexposed are at risk)

22
Q

interpretation of incidence rate ratio

A

patients will get disease IRR times faster if exposed

23
Q

hazard rates

A

similar to incidence rate but estimated from a type of statistical model that estimates time to event of interest in different groups

24
Q

cohort study uses

A

good for COMMON diseases to calculate RISK RATIO

start with population at risk (disease free) –> determine exposure

25
Q

why can you calculate risk ratio of a cohort study

A

because samples are randomly selected (all subjects are disease free at enrollment)

26
Q

limitations of cohort studies

A

rare diseases make it difficult because you would have cases «< controls

inefficient to follow all controls just to find an adequate number of cases
- can compare the cases to a smaller sample of controls and statistically still get the same results

27
Q

case control study uses

A

similar enrollment as cohort study except controls are sampled from the cohort
- allows study of RARE diseases

cases: enrolled from the cohort if they develop the disease over a set time period

controls: enrolled from the cohort if they are at risk of getting the disease but do not have it yet

28
Q

can you calculate risk ratio from a case control study

A

NO because the number of cases and controls were selected by the investigator (not randomly sampled like cohort)

subjects are STARTING with disease vs no disease

29
Q

case control study steps

A
  1. start with a cohort
  2. determine the marginal totals of cases and controls (sampled from cohort)
  3. determine exposure status of cases and controls
30
Q

what can be calculated from case control studies

A
  • odds of exposure
  • case control (exposure) odds ratio
31
Q

odds of exposure

A

probability of being exposed / probability of not being exposed

p / 1-p where p = probability

32
Q

odds of exposure among cases

A

proportion of cases exposed / proportion of cases not exposed

(A / A+B) / (B / A+B)
=
A / B

33
Q

odds of exposure among controls

A

proportion of controls exposed / proportion of controls not exposed

(C / C+D) / (D / C+D)
=
C /D

34
Q

case control odds ratio

A

odds of exposure among cases / odds of exposure among controls

exposure odds ratio

(A/B) / (C/D)
=
AD / BC

35
Q

can risk ratio be calculated from a case control study

A

NO - but can be approximated from the case control odds ratio

risk ratio = disease odds ratio = case control odds ratio ONLY when the disease is rare

36
Q

can you calculate risk from a case control study

A

NO and you can NOT approximate it either

can only approximate RISK RATIO (relative risk)

37
Q

exposure odds ratio vs disease odds ratio

A

EOR: measured in case control studies

DOR: measured in cohort studies

38
Q

how are EOR and DOR related

A

EOR is always equal to DOR

39
Q

how are DOR and risk ratio related

A

DOR = risk ratio (relative risk) when the disease is RARE

40
Q

when is a disease considered rare

A

when risk < 5% in a period of time

odds is bound from 0 to infinity
risk is bound from 0 to 1
when p = 0.05 –> odds curve diverges from probability/risk curve –> odds ratio no longer equals risk ratio

41
Q

how are controls selected for a case control study

A

3 rules
1. control should only be selected if someday, if it were to become a case, then it would be eligible to be included in the study as a case
2. controls should be selected for reasons unrelated to exposure
3. select incident (new) cases NOT prevalent (old) cases

42
Q

how many controls should be enrolled in a case control study

A

want to have a minimum of 1 control per case

more controls per case is better, but no need for >4 cases per control

43
Q

what is the use of case control studies

A

hypothesis generating - examine a large number of exposures for one outcome/disease

VET 414: Population Health (17 decks)

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