Lectures 1&2 - The importance of evidence in the practice of medicine

Question 1

what is evidence based medicine?

Answer 1

the use of critically appraised info to determine strength of evidence for the use of treatments and medicine in clinical practice

Question 2

outline the different stages of clinical medicine where EBM can be of use

Answer 2

CLINICAL FINDINGS- use of patient history and physical exam
AETIOLOGY - identifying cause of disease
CLINICAL MANIFESTATIONS OF DISEASE - how often & when a disease causes clinical problems
DIFFERENTIAL DIAGNOSIS - selecting likely, serious and treatment-responsive causes of a problem
DIAGNOSTIC TESTS - selecting and interpreting tests to confirm/exclude diagnoses
PROGNOSIS - estimating a patient’s clinical course and anticipating complications
THERAPY - selecting treatments that are cost effective and where good > harm
PREVENTION - reducing chance of disease by identifying and modifying risk factors and use of screening in early diagnosis

Question 3

what are the criticisms of EBM?

Answer 3

• not enough time for doctors to critically appraise info

- EBM has been inappropriately used by the gov’t to justify decisions that clinicians disagree with

Question 4

what is the importance of EBM?

Answer 4

• better service to patients
• better patient care & safety
• increased medical knowledge
• revalidation - clinicians are up to date with evidence
• professionalism
• better interpersonal & communication skills

Question 5

list the order of the hierarchy of studies

Answer 5

1) meta-analyses & systematic reviews
2) RCTs
3) cohort studies
4) case-control studies
5) cross sectional studies
6) animal trials & in-vitro studies
7) case reports, opinion papers, letters

Question 6

describe systematic reviews & meta-analyses

Answer 6

• systematic reviews answer a defined research question by collecting and summarising evidence
• meta-analysis refers to use of statistical techniques to integrate the results of studies that match the eligibility criteria
• cheap
• avoids issue of large sample size as data for the study is pooled from many smaller studies

Question 7

describe RCTs

Answer 7

• strong inclusion/exclusion criteria
• requires a large sample size
• expensive

Question 8

describe cohort studies

Answer 8

• involves a group of people before they develop a condition
• exposures and risk factors are observed
• group is followed up over a period of time to see who ends up suffering from disease
• more effective with common diseases
• less prone to bias
• can be prospective or retrospective

Question 9

describe case-controlled studies

Answer 9

• involves people suffering from disease and people not suffering from disease (control)
• more useful for rare conditions
• quick and cost-efficient
• can investigate many exposures simultaneously
• selection bias
• recall (of information) bias
• poor for rare exposures

Question 10

describe ecological studies

Answer 10

• descriptive/observational study

- used to measure prevalence and incidence of disease in different populations, particularly when disease is rare

Question 11

describe cross sectional studies

Answer 11

• routinely collected data that helps to describe the status of individuals with respect to absence/presence of both exposure and disease assessed at the same point in time
• hard to establish causal effect

Question 12

describe case reports

Answer 12

• description of single case
• not used to support clinical practice
• may be useful in picking out new syndromes/conditions

Question 13

what is association?

Answer 13

the statistical dependence between 2 variables - the degree to which the rate of disease in persons with a specific exposure is higher/lower than the rate of disease without the exposure

Question 14

what 4 things can be used to evaluate statistical association?

Answer 14

Chance
Bias
Confounding factors
Causal effect

Question 15

how is chance used to evaluate statistical association?

Answer 15

• how big is the sample size?
• use of power calculations - minimum sample size required so that you can likely detect an effect of a given size
• p values - p < 0.05 = low p that it’s due to chance = significant
  confidence intervals - range within which the ‘true’ value is expected to lie with a given degree of certainty

Question 16

how is bias used to evaluate statistical association?

Answer 16

bias is a consequence of defects in design/execution (systemic error)

• selection bias - selection of participants
• measurement bias - measurements/classifications of disease/exposure

Question 17

how are confounding factors used to evaluate statistical association?

Answer 17

factors that distort risk of disease but do not alone cause disease

• age
• sex
• socio-economic
• geography

Question 18

how is causal effect used to evaluate statistical significance?

Answer 18

judgement of a cause-effect relationship based on logic -> observed association between exposure and disease -> sufficient evidence

Question 19

outline the factors to consider in the Bradford-Hill Criteria for causation

Answer 19

ANALOGY - there is a source of more elaborate hypotheses about the association
STRENGTH - of association, measured by magnitude of relative risk
SPECIFICITY - if an exposure increases the risk of 1 disease but not many diseases
EXPERIMENTAL EVIDENCE - evidence on humans/animals
TEMPORAL RELATIONSHIP(!) - risk factor causes disease if it precedes the disease
CONSISTENCY - similar results in different populations using different study designs
DOSE-RESPONSE RELATIONSHIP - increased exposure = increased risk of disease
PLAUSIBILITY - association is more likely to be causal if consistent with other knowledge
COHERENCE - information is not conflicting

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