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evidence based medicine terminology Flashcards

Research and evidence-based medicine. In: Murtagh J, Rosenblatt J, Coleman J, Murtagh C. eds. Murtagh's General Practice, 7e. McGraw-Hill; Accessed February 24, 2021. https://murtagh.mhmedical.com/content.aspx?bookid=2471§ionid=199053198

1
Q

EBM - what is a ‘valid’ method

A

a method that measures what it claims to measure

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2
Q

EBM - difference between internal and external validity

A

internal validity refers to how well it measures the things in the studied population

external validity refers to how generalisable it is to the general population

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3
Q

EBM - what is a ‘true positive’ in a diagnostic test

A

a positive test result in a patient(s) who have the disease

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4
Q

EBM - what is a ‘true negative’ in a diagnostic test

A

a negative test result, in a patient without disease

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5
Q

EBM - what is a ‘false positive’ in a diagnostic test

A

a positive test result in a patient who does not have disease

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6
Q

EBM - what is a ‘false negative’ in a diagnostic test

A

a negative test result in a patient who has a disease

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7
Q

EBM - how do you calculate the positive predictive value of a diagnostic test

A

A / (A + B)
where
A = True Positive
B = False Positive

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8
Q

EBM - how do you improve the positive predictive value of a diagnostic test

A

reduce the amount of false positives

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9
Q

EBM - how do you calculate the negative predictive value of a diagnostic test

A

D / (C + D)
where
D = True negative
C = False negative

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10
Q

EBM - how do you improve the negative predictive value of a diagnostic test

A

reduce the amount of false negatives

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11
Q

EBM - what are the implication of a positive test result in a test with high positive predictive value

A

higher PPV = lower chance of false positive -> likelier that disease is present

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12
Q

EBM - what are the implications of a negative test result in a test with high negative predictive value

A

higher NPV = lower chance of false negative -> likelier that disease is not present

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13
Q

EBM - how do you calculate sensitivity of a diagnostic test

A

A / (A + C)
where
A = True Positive
C = False negative

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14
Q

EBM - how do you calculate specificity of a diagnostic test

A

D / (B + D)
where
D = true negative
B = false positive

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15
Q

EBM - what does sensitivity of a diagnostic test measure

A

proportion of diseased people with a positive test result

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16
Q

EBM - what does specificity of a diagnostic test measure

A

how often a test is negative, when there is no disease present

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17
Q

EBM - how do you improve the sensitivity of a diagnostic test

A

increase the amount of true positives measured

reduce the amount of false negatives measured

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18
Q

EBM - how do you improve the specificity of a diagnostic test

A

increase the amount of true negatives measured

reduce the amount of false positives measured

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19
Q

EBM - why is a negative result in a sensitive test good at ruling out disease

A

sensitive tests have few false negatives. So if the result is negative, its more likely to be a true negative

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20
Q

EBM - why is a positive test result in a specific test good at ruling in disease

A

specific tests have few false positives. So if the result is positive, its more likely to be a true positive

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21
Q

EBM - define incidence

A
  • number of new cases measured,
  • in a defined population
  • over a defined time period
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22
Q

EBM - define prevalence

A
  • number of known cases in a population / number of people in that population
23
Q

EBM - what is bias

A

any effect that occurs during research, that leads to measurements that depart systematically from the true values

24
Q

EBM - what is selection bias

A

investigating a sample that is not representative of the population as a whole

25
Q

EBM - how does bias affect the validity of a study

A

it loses internal validity

26
Q

EBM - what is recall bias

A

bias that occurs from sample population’s recollection; can be

  • people with the outcome being more likely to recall an exposure
  • people with an exposure being more likely to identify the outcome as occurring
27
Q

EBM - what is observer bias

A

bias that occurs from the investigator’s measurements; by measuring the outcome differently given they are aware of the studied individual’s exposure status

28
Q

EBM - what type of study is most likely to suffer from recall and observer biases

A

case-control studies

retrospective cohort studies

29
Q

EBM - what is a systematic error in measurement

A

an error that has a predictable, constant or proportional effect on measuring the true value

30
Q

EBM - what is random error in measurement

A

deviations from true value caused by fluctuations in measurement

31
Q

EBM - how do you compensate for random error in measurement

A

do multiple measures and take average

32
Q

EBM - how do you compensate for systematic error in measurement

A

change study design so the error can’t occur

33
Q

EBM - what effect do systematic errors have on the validity of a study

A

reduces the internal validity of a study

34
Q

EBM - what is a type I error

A

an error where a study concludes there is a difference between 2 groups, but there isn’t in reality

35
Q

EBM - what is a type 2 error

A

an error where a study concludes there is no difference between 2 groups, but there is in reality

36
Q

EBM - clinical study design - broadly, the 2 types of study designs classified by how they handle exposures

A

observational studies - exposure is not modified by scientists
experimental / interventional studies - the exposure is modified by scientists

37
Q

EBM - clinical study design - what is a case report

A

a report on a single patient with a particular disease or outcome, may go backwards to explore their exposures

38
Q

EBM - clinical study design - what is a case series

A

a report on a group of patients with a particular disease or outcome, may go backwards to explore their exposures

39
Q

EBM - clinical study design - what is a cross-sectional study

A

prevalence study ie looks at how many people in a population have a disease, and characteristics of the population

40
Q

EBM - clinical study designs - what is the difference between, and similarities between, descriptive and analytic studies

A

descriptive and analytic are both observational ie you don’t mess with any of the exposures, just record whats observed

analytic studies will compare 1 group against another, whereas a descriptive study just tells you what happens in a particular group of people

analytic studies allow you to make inferences (hypotheses) to compare 1 group against another

41
Q

EBM - clinical study design - what is a case control study

A

Take a group of people with a disease
Take a matched group of people without the disease
look back and check their exposures

42
Q

EBM - clinical study design - what type of analytic study is ideal for rare disease, why

A

case controls; their design is outcome -> exposure, so you can recruit sufficient people

43
Q

EBM - clinical study design - what is a diagnostic accuracy study

A

a type of study that compares the diagnostic accuracy of a new investigation test, against a gold standard test

44
Q

EBM - clinical study design - what type of study are diagnostic accuracy studies usually classed as

A

case-control studies
- you have a group of people with the disease, and without the disease
- you are then comparing test results between the 2
outcome -> exposure

45
Q

EBM - clinical study design - what is a cohort study

A

a study where you take 2 or more populations with / without an exposure, and assess whether they have a particular outcome over a time period

46
Q

EBM - clinical study design - what is an audit

A

an audit is a study that measures current standard of care against an ‘ideal’ standard, usually a guideline.

Can also measure whether the ‘right results’ are produced ie outcomes are changing

47
Q

EBM - what is a ‘null hypothesis’

A

means that the relationship between 2 data points is occurring by chance ie they are not related

48
Q

EBM - what does it mean to ‘reject the null hypothesis’

A

rejecting it means that that the 2 data points measured have a relationship to one another

49
Q

EBM - how to calculate risk

A

(number of events in a group) / (number of members of a group)

50
Q

EBM - how to calculate odds

A

(number of members who had the event) / (number of members who did not have the event)

51
Q

EBM - how to calculate a risk ratio

A

consider 2 groups - one had an intervention (I), the other did not (C)
risk in intervention = (number of intervened people with outcome) / (number of people intervened)
risk in control = (number of controlled people with outcome) / (number of people in control)

risk ratio = risk in intervention / risk in control

52
Q

EBM - how to calculate an odds ratio

A

consider 2 groups - one had an exposure (E), the other had no exposure (N)
odds in exposure group = (number of people exposed with outcome) / (number of people exposed without outcome)
odds in non-exposure group = (number of people unexposed with outcome) / (number of people unexposed, without outcome)

odds ratio = odds in exposure group / odds in non-exposure group

53
Q

EBM - why can’t you calculate a risk ratio in a case-control study

A

we’re going from outcome -> exposure, so we don’t actually have an idea of how many people are in the exposure group

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