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FRACP > EBM > Flashcards

EBM Flashcards

1
Q

What is Cox proportional hazards analysis used for?

A

Compares dichotomous outcomes, except that time itself may be a variant.

Similar to logistic regression multivariant analysis (but time cannot be variant with this)

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2
Q

How is ARR (absolute risk reduction calculated) given the AE rate in placebo and treated groups?

A

ARR = AE rate in placebo (higher) – AE rate In treated (lower)

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3
Q

What is publication bias?

A

Publication bias is due to journals only publishing positive results.

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4
Q

Given the incidence of disease in the exposed is 0.10 and unexposed is 0.02. Calculate the RR (relative risk)

A

RR is an incidence ratio

RR = incidence of exposed (higher) / incidence of unexposed (lower)

RR = 0.10 / 0.02 = 5

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5
Q

How does the clinical utility of sensitivity/specificity differ from PPV/NPV?

A

Difference in clinical utility:

Sensitivity / Specificity = population studies

PPV / NPV = more relevant to the individual

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6
Q

Describe the calculation of specificity.

A

Specificity (column) = TRUE negative / ALL without disease

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7
Q

Describe the calculation of sensitivity.

A

Sensitivity (column) = TRUE positive / All with disease

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8
Q

Which of the predictive values (i.e. PPV/NPV) is 100% for the following:

  1. Sensitivity
  2. Specificity
A

1, If sensitivity = 100% then NPV = 100%

  1. If specificity = 100% then PPV = 100%

NB: think converse!

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9
Q

What does ANOVA analysis compare?

A

ANOVA compares >2 means

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10
Q

Compare type 1 (alpha) and type 2 (beta) statistical errors.

A

Statistical errors:

Type I (alpha) error:

  • Denial of truth
  • REJECTION of the a TRUE null hypothesis
  • p-values

Type II (beta) error:

  • Acceptance of falsehood
  • FAILURE to reject (i.e. acceptance of) a FALSE null hypothesis
  • Power
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11
Q

How is (OR) odd ratio calculated?

A

OR = (true positive x true negative) / (false positive x false negative)

‘Truth over lies’

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12
Q

Describe the differences in statistical analyses for variable that are discrete vs continuous (dependent vs independent).

A

Types of statistical analysis:

  1. Comparing 2 discrete variables = chi-squared
  2. t-tests are for continuous variable:

a. Unpaired – for independent groups e.g. birthweight in males and females.
b. Paired – for dependent groups e.g. pre- and post- BPs.

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13
Q

What is the fundamental difference between multiple regression multivariant analysis vs. logistic regression multivariant analysis?

A

Multiple regression multivariant analysis: compares multiple outcomes that are continuous e.g. BP

Logistic regression multivariant analysis: compares multiple outcomes that are dichotomous e.g. alive vs. dead

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14
Q

Considering a normally distributed population, what percentage of a population lie within:
1x SD
2x SD

A

For normal distribution:
66% within 1x SD
95% within 2x SD

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15
Q

Give the formulae for likelihood ratios LR+ and LR-

A

LR+ = sensitivity / (1-specificity)

LR- = (1-sensitivity) / specificity

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16
Q

Describe the calculation for NPV and PPV.

A

NPV (row) = TRUE negative / ALL test negative

PPV (row) = TRUE positive / ALL test positive

17
Q

What is the difference between attributable/absolute risk and relative risk?

A

Attributable/Absolute risk (risk difference) = incidence of disease in UNexposed – incidence of disease in exposed

Relative risk (risk ratio) = incidence of disease in exposed / incidence of disease in Unexposed

18
Q

What is the difference between SD and SEM?

A

SD: measure variability of data around a mean
SEM: measures the variability of a sample mean with respect to the likelihood of it being the true mean

SEM is not the same as SD

19
Q

True/False: prevalence of disease plays an important role in the calculation of NPV and PPV.

A

True

20
Q

What is an example of observation/measurement bias?

A

Example of observation/measurement bias: recall of weight by patients vs. actually measuring it.

21
Q

What is the difference between intention-to-treat and per-protocol statistical analyses?

A

Intention-to-treat = analysis according to original designations (more realistic)

Per-protocol = analysis according to actual treatment received

22
Q

What is an example of selection bias?

A

Example of selection bias: enrolment of hospitalised patient only with bias towards a sicker population of patients.

23
Q

Describe the Kaplan-Meir curve.

A

Kaplan-Meir curves calculate the ratio of surviving patients divided by the total number of at-risk patients. Ratio is recalculated everytime the patient has an outcome.

24
Q

What is lead time bias?

A

Lead time bias occurs in screening when the patient is diagnosed early by virtue of a screening process and therefore may have an artificially lengthened survival time that is not a function of the natural history of the disease or intervention.

25
Q

The incidence of a disease is 2.5% in a population exposed to a protective factor/treatment and 3% in those not exposed to the protective for/treatment. Calculate the following:

  1. ARR
  2. NNT
  3. RR
A

Incidence exposed = 0.025 and incidence UNexposed = 0.03

ARR = 0.03-0.025 = 0.005 = 0.5% [Unexposed – exposed]

NNT = 1/0.005 = 200 people[1/ARR]
RR = 0.025/0.030 = 83% [exposed/Unexposed]
26
Q

Incidence of disease in a population exposed to a risk factor is 10% and incidence in a population unexposed is 2%. What is the relative risk?

A

RR = incidence exposed / incidence UNexposed = 0.1/0.02 = 5

RR is an incidence ratio

27
Q

Given the AE rate for a placebo group and treated groups, how does one calculate the ARR?

A

ARR = AE rate in placebo group – AE rate in treated group

28
Q

How is post-test probability calculated?

A
  1. Calculate LR+ = sensitivity / (1 - specificity)
  2. Pre-test odds = prevalence / (1 - prevalence)
  3. Post test odds = pre-test odds x LR+

Convert post-test ODDS to post-test probability:

  1. Post-test probability - post-test odds / (1 + post-test odds)

FRACP (20 decks)

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