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Critical appraisal of papers PHM > Lecture > Flashcards

Lecture Flashcards

1
Q

What is equipoise?

A

the assumption that there is not one better intervention present during the design of a RCT

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2
Q

what are the types of evidence?

A

trials and studies

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3
Q

what are trials?

A

involves an intervention -> measure an outcome

gold standard = randomised double blinded controlled trial

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4
Q

what are studies?

A

observational, no intervention

Diagnostic - how good a diagnostic test is

Prognostic - look at rf on outcomes often of cohort study

Case control - retrospective, two groups of different outcomes

Cohort study - group of people. prospective

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5
Q

what levels of evidence are 1a/1b?

A

Ia: systematic review/meta-analysis of RCTs

Ib: at least one rct

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6
Q

what level of evidence are IIa/IIb?

A

IIa: at least one well-designed controlled study without randomisation

IIb: at least one well-designed quasi-experimental study such as a cohort study

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7
Q

what is a quasi experiment?

A

subject to concerns regarding internal validity, because the treatment and control groups may not be comparable at baseline. With random assignment, study participants have the same chance of being assigned to the intervention group or the comparison group

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8
Q

what level of evidence is III?

A

III: well designed, non-experimental descriptive study eg comparative study, correlation, case-control study, case series

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9
Q

what level of evidence is IV?

A

opinions and/or clinical experience

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10
Q

What are the levels of evidence?

A

Ia (highest)

IV (lowest

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11
Q

What is phase 1 of trials?

A

safety testing of new med on few (often) healthy volunteers - establish side effect profiles

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12
Q

What is phase 2 of trials?

A

testing on larger groups of disease patients - establish idea of efficacy and further side effects

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13
Q

what is phase 3 of trials?

A

large comparison trials on disease patients - for robust efficacy data in comparison to existing treatment

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14
Q

what is efficacy?

A

the ability to produce a desired or intended result

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15
Q

what is a null hypothesis? (Ho)

A

there is no difference between the two groups, any difference between these two groups is due to chance

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16
Q

what is the alternative hypothesis?

A

there is a difference between the two groups

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17
Q

what is the p value?

A

probability of detecting a difference with a priori assumption that the null hypothesis is true

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18
Q

what is the p value set at?

A

5% or 0.05

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19
Q

what does it mean if p value <0.05?

A

consider such a low probability that there must be an error in the logical argument - the error is considered to be in the priori assumption, therefore the null hypothesis cannot be true so the alternative hypothesis must be true

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20
Q

what are the limitations of hypothesis testing?

A 
the amount of difference is not stated
simple binary (yes/no) answer
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21
Q

what is the estimation?

A

we can never know true difference between two groups in a population so we take a sample - estimate the difference between the two groups using the data from the sample

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22
Q

what is the absolute difference?

A

the difference found in a study = estimation of the whole population

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23
Q

what is the true difference?

A

the actual difference in population

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24
Q

how can the estimation be presented?

A
  1. as a number
  2. as an absolute difference
  3. as a ratio
  4. as a proportion
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25
Q

what are confidence intervals?

A

is the range around the estimation

normal 95% CI = the range between which there is 95% chance that the true value will lie

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26
Q

what are the units of no effect in confidence intervals?

A

with absolute difference - no difference would be 0

with a ratio - no difference would be 1

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27
Q

what is good about confidence intervals?

A

width of interval indicates PRECISION of estimate

can be used to estimate type 2 statistical error

indicates lack of statistical significance if interval crosses unit of no effect

gives info of size and direction of difference

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28
Q

what is a type 2 statistical error?

A

the study has shown that there is no statistically significant difference in the groups but in the real world there might be (false negative)

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29
Q

what is the primary outcome?

A

the variable outcome of most interest

any difference in outcome between the groups is believe to be due to the intervention

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30
Q

what is the minimum clinically important difference?

A

the least difference outcome that is clinically important -

looking at the clinical significance with statistical significance

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31
Q

what is the intervention?

A

what we do to the patient that can change things

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32
Q

what are time points to measure?

A

when the outcome is measured

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33
Q

what is the power of a study?

A

the probability that a trial will detect a difference that truly exists

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34
Q

what does the power calculation look at?

A

type 1 error: finding a difference when there isn’t one in real life (false positive) = ALPHA

type 2 error: not finding a difference when there is one (false negative) = BETA

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35
Q

power is dependent on what four things?

A
  • probability of T1 error (0.05) [ALPHA]
  • sample size
  • standard deviation of sample
  • minimal clinically significant difference
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36
Q

what does power equal (calc)

A

1-beta

beta = probability of getting a type 2 error

37
Q

what is a type 1 error?

A

false positive

incorrectly rejecting null hypothesis

experiment shows significant difference when the null hypothesis is true (no difference in actual population)

probability of type 1 error = alpha

38
Q

what is a type 2 error?

A

false negative

incorrectly accepting null hypothesis

experiment does not show significant difference when the alternative hypothesis is true (there is a difference in actual population)

probability of type 2 error = beta

39
Q

what is type 1 error due to?

A
  • bias
  • confounding factors
  • multiple hypothesis testing
40
Q

what is type 2 error due to?

A

sample size

41
Q

what is sample size?

A

number of participants required to detect a difference of a specified size

42
Q

what is screening?

A

physically identifying potentially eligible participants

43
Q

what criteria do you use when screening patients?

A

inclusion/exclusion

  • every pt that fulfils inclusion criteria must be recorded
  • everyone must have exclusion criteria applied -> if not, must record why
44
Q

what is allocation concealment?

A

allocation sequence is concealed from all staff (reducing selection bias)

45
Q

what is randomisation?

A

process of assigning to groups with known chance for each participant to enter any group (reduces allocation bias)

equally distribute confounders

46
Q

what is blinding?

A

treatment assignment is concealed (reduces ascertainment bias)

concealment if whether in placebo group or not

47
Q

how do you get ethics for your research?

A

submit protocols to REC/IRB for approval

48
Q

what are the types of data?

A

continuous

categorical

49
Q

what is reported in continuous data?

A

normally distributed - mean and standard deviation

non-normally distributed - median and inter-quartile range

50
Q

what is categorical data?

A

nominal (without order) e.g. colour, gender

ordinal (with order) e.g. scale - slow, medium, fast

51
Q

what is intention to treat analysis?

A

analysis includes every subject who is randomized according to randomized treatment assignment. It ignores noncompliance, protocol deviations, withdrawal, and anything that happens after randomization

52
Q

what is imputation for missing data?

A

replacing missing data with substituted values

53
Q

what are the measurements of central tendency?

A

mean
median
mode

54
Q

what is the mean?

A

the average

used in normally distributed data
SD measured

55
Q

what is the median?

A

central value

use if data is skewed
IQR measured

56
Q

what is the mode?

A

most frequent value

rarely used

57
Q

what are the techniques for comparing groups?

A

categorical: chi-squared (X2)
continuous: depends on distribution - T-test, ANOVA

58
Q

does funding need to be stated?

A

yes - all funding needs to be clearly stated and role of funders

59
Q

what is enrolment?

A

if they fit inclusion criteria - sign consent (NOK if don’t have capacity or PLR by nurse/doctor)

60
Q

what is risk?

A

the probability of an event occurring

61
Q

what is the absolute risk reduction? (ARR)

A

the difference between the event rate in the treatment group and the event rate in the control group

(event rate in control group) - (event rate in treatment group)

62
Q

what is numbers needed to treat?

A

the number of patients that need to be exposed to intervention for one of them to sustain the effect

1/ARR

63
Q

what is the risk ratio? aka relative risk

A

ratio of risk of outcome in treatment group to risk of outcome in control group

RR > 1 then the risk of the event in the treatment group occurring is great than the rate in the control group

RR<1 the risk of event in the treatment group occurring is less than the rate in the control group

(event rate in treatment group)/(event rate in control group)

64
Q

What is the relative risk reduction?

A

the proportion by which the intervention reduces the outcome rate

watch out for high RRR in events that are rare

e.g. increased risk of breast cancer in young women due to OCP - high RRR, low ARR

proportion of ARR to the control event rate

(CER-EER)/CER

65
Q

What are odds?

A

another way to express chance

the ratio of the number of times an event occurs to the number of times it does not occur

the odds of rolling a six on a dice = 1/5 =0.2

(NB risk of rolling a six = 1/6)

66
Q

what is an odds ratio?

A

ratio of odds of event in treatment group to odds of an event in control group

expresses how much more likely the event will occur in treatment group in comparison to control

>1 = the event rate is greater in the treatment group
<1 = the event rate is greater in the control group
67
Q

what is accuracy?

A

inaccuracy is due to systematic error (bias)

an accurate study hits bullseye every time but have poor spread within bullseye

68
Q

what is precision?

A

imprecision due to random error (chance)

precise study has closely clustered results but may not in the gold

69
Q

what is accuracy in a test?

A

the proportion of patients correctly identified by the test (true positives and true negs)

70
Q

what is the reference standard in 2x2 diagnostics?

A

definition of having the disease for the purposes of the paper

71
Q

what is the gold standard?

A

definition of having the disease as recognised by international medical community

72
Q

what is sensitivity?

A

proportion of patients with the disease that have a positive test

ability of a test to correctly classify patients as having disease

true positive/(true positive + false negative)

73
Q

what is specificity?

A

proportion of patients without the disease that have a negative test

ability of test to correctly classify patients as not having disease

true neg/(false pos + true neg)

74
Q

What is SpIn?

A

Rule in a disease

Test with high specificity (with few false positives) accurately rules in the diagnosis

75
Q

what is SnOut?

A

Want to rule out disease

Test with high sensitivity (few false negatives) accurately rules out a diagnosis

76
Q

does changing the population prevalence change the sens/specificity?

A

nope - about the test

77
Q

what is the positive predictive value?

A

proportion of patients with positive test that have disease

true pos/(true pos + false pos)

78
Q

what is the negative predictive value?

A

proportion of patients with neg test that do not have disease

true neg/(false neg + true neg)

79
Q

will PPV and NPV change with population prev?

A

yes - about the patient

80
Q

What happens to PPV and NPV when the prevalence increases?

A

PPV rises
NPV drops

Sens/spec stay the same

81
Q

What kind of diagnostics do we use in ED?

A

Usually use tests to RULE OUT a diagnose more often than to rule in

so often have high SENSITIVITY (SnOut) and low specificity

82
Q

What do you want in order to diagnose something?

A

high positive predictive value

but low prevalence gives low PPV so need to perform initial test on population that has a high prevalence -> aka screening

83
Q

What is a likelihood ratio?

A

(probability of individual with condition having the test result)/(probability of an indiv without the condition having the test result)

84
Q

How do you measure likelihood ratio for positive test?

A

sensitivity/(1-specificity)

85
Q

How do you measure the likelihood ratio for negative test?

A

(1-sensitivity)/specificity

86
Q

What does the likelihood ratio measure?

A

how much more likely (for positive) or less likely (negative) than the pre-test probability is it that a patient has the disease

87
Q

what is a receiver operating characteristic curve?

A

another way of gauging the usefulness of a diagnostic test

x-axis: 1-specificity
y-axis: sensitivity

want each to be perfect = 1

88
Q

what does the area under the curve represent?

A

the closer to 1 - the better the test
(between 0.5 and 1)
the bigger the area - the better the test

Critical appraisal of papers PHM (1 decks)

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