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AKT > Statistics > Flashcards

Statistics Flashcards

1
Q

Define specificity

A

Proportion of patients without the condition who have a negative result

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2
Q

Formula for specificity

A

TN / TN + FP

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3
Q

Define sensitivity

A

Proportion of patients with the condition who have a positive test result

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4
Q

Formula for sensitivity

A

TP / TP + FN

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5
Q

Define positive predictive value

A

The chance that the patient has the condition if the diagnostic test is positive

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6
Q

Formula for positive predictive value

A

TP / TP + FP

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7
Q

Define negative predictive value

A

The chance that the patient does not have the condition if the diagnostic test is negative

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8
Q

Formula for negative predictive value

A

TN / TN + FN

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9
Q

Define likelihood ratio for a positive test result

A

How much the odds of the disease increase when a test is positive

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10
Q

Formula for likelihood ratio for a positive test result

A

sensitivity
/
(1 - specificity)

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11
Q

Define likelihood ratio for a negative test result

A

How much the odds of the disease decrease when the test is negative

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12
Q

Formula for the likelihood ratio for a negative test result

A

(1 - sensitivity)
/
specificity

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13
Q

Which significance tests are used on parametric data?

A

Student’s t- test (paired or unpaired)

Pearson’s product-moment coefficent (for correlation)

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14
Q

Which significance test is used on non-parametric data for comparing ordinal, interval or ratio scales of unpaired data?

A

Mann-Whitney U test

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15
Q

Which significance test is used on non-parametric data comparing two sets of observations on the same sample (e.g. before and after)

A

Wilcoxon signed-rank test

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16
Q

Which significance test is used to compare proportions or percentages on non-parametric data?

A

Chi-squared test

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17
Q

Which significance test is used for measuring correlation in non-parametric data?

A

Spearman, Kendall rank

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18
Q

Relationship between mean, median and mode in normal distributed data

A

mean = median = mode

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19
Q

Relationship between mean, median and mode in positively skewed data

A

mean > median > mode

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20
Q

Relationship between mean, median and mode in negatively skewed data

A

mean < median < mode

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21
Q

What is the goal of a phase 1 trial?

A

Determine pharmacokinetics and pharmacodynamics and side effects

Small study on healthy volunteers

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22
Q

What is the goal of a phase 2 trial?

Goals of 2a and 2b trials

How many patients?

A

Assess dosage and efficacy

2a = dosage
2b = efficacy

Small number of patients affected by disease

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23
Q

What is the goal of phase 3 trial?

A

Assess effectiveness

Large RCT comparing new treatment to old

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24
Q

What is the goal of a phase 4 trial?

A

Monitoring long term effectiveness and side effects

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25
Q

Formula for numbers needed to treat

A

1 / (absolute risk reduction)

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26
Q

How to calculate the absolute risk reduction

A

Control event rate - experimental event rate

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27
Q

How to calculate the control event rate

A

number who had outcome with control / total number who had the control

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28
Q

How to calculate the experimental event rate

A

number who had outcome with the intervention / total number who had the intervention

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29
Q

What is the usual outcome measure for a cohort study?

A

Relative risk

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30
Q

What is the usual outcome measure for a case-control study?

A

Odds ratio

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31
Q

What does endemic mean?

A

Persistent, usual or expected level of disease in a given population

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32
Q

How to calculate the relative risk

A

EER / CER

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33
Q

How to calculate the relative risk reduction or relative risk increase

A

EER - CER / CER

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34
Q

What is a type 1 error?

A

The null hypothesis is rejected when it is true

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35
Q

What is a type 2 error?

A

The null hypothesis is accepted when it is false

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36
Q

What is the name given to a phenomenon where if a variable is extreme on its first measurement, it will tend to be closer to the average on its second measurement

A

Regression

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37
Q

What statistical test to use on data with several groups?

A

ANOVA

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38
Q

What is ANOVA used for?

A

Comparing the variance of the means

Several groups of data

Normally distributed data

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39
Q

What is a spurious association?

A

Arisen by chance and not real

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40
Q

What is an indirect association?

A

Association is due to another factor (a confounding variable)

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41
Q

What is a direct association?

A

True association not linked by a third variable

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42
Q

What criteria are use to establish causation?

A

Bradford Hill Causal Criteria

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43
Q

How to calculate standard deviation

A

√variance

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44
Q

How to calculate standard error of the mean

A

standard deviation / √n

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45
Q

What is confounding?

A

A variable that correlates to other variables within a study, leading to spurious results

46
Q

How can you control confounding at the design stage of an experiment?

A

Randomisation

47
Q

How can you control confounding at the analysis stage of an experiment?

A

Stratification

48
Q

What is nominal data?

A

Values put into categories with no order e.g. birth place

49
Q

What is ordinal data?

A

Values put into categories which can be ordered e.g. NYHA classification of heart failure

50
Q

What is discrete data?

A

Values confined to certain values e.g. number of asthma exacerbations per year

51
Q

What is continuous data?

A

Data can take any value within a certain rage e.g. weight

52
Q

What is binomial data?

A

Data may take one of two values e.g. gender

53
Q

What is the delphi method?

A

Method of asking for then collating expert opinion

54
Q

Issues with the delphi method

A

Time consuming
Low response rates
Investigators can mould responses
Expertise of the panelists could be unevenly distributed

55
Q

What is the hierarchy of medical evidence?

A

1) Metanalysis of RCT
2) 1x RCT
3) Systematic reviews of cohort studies
4) Cohort studies
5) Systematic reviews of case-control studies
6) Case-control studies
7) Case series
8) Expert opinion

56
Q

When is hazard ratio used?

A

When analysing survival over time

57
Q

What is used to measure general practice workload?

A

Jarman Underprivileged Area Score

58
Q

What % of values lie within 1 SD of the mean?

A

68.3%

59
Q

What % of values lie within 2 SD of the mean?

A

95.4%

60
Q

What % of values lie within 3 SD of the mean?

A

99.7%

61
Q

What % of values lie within 1.96 SD of the mean?

A

95%

62
Q

What is the power of a study?

A

Probability of correctly rejecting the null hypothesis when it is false

63
Q

How is power calculated?

A

1 - probability of a type 2 error

64
Q

What is the p value?

A

the probability of obtaining a result by chance as least as extreme as the one that was observed, assuming the null hypothesis was true

65
Q

What does reliability assess?

A

Consistency

66
Q

What does validity assess?

A

Accuracy

67
Q

What error is the p value equal to?

A

Type 1 error

68
Q

Equivalence trial

A

Equivalence margin of -delt to +delta

If CI lies within equivalence margin then drugs have similar effect

69
Q

What are independent variables?

A

Something that is purposefully changed by the researcher

70
Q

What are dependent variables?

A

The one that is observed and changes in response to the independent variable

71
Q

What are controlled variables?

A

All other variables that are not the dependent variable or the independent variable

Do not change throughout the study

72
Q

What is the population attributable risk?

A

Reduction in incidence if the population were entirely unexposed

73
Q

What is the attributable proportion?

A

Proportion of the disease that would be eliminated if the disease rate were reduced to that of the unexposed group

74
Q

What is a case control study?

A

Retrospective

Participants with condition are identified and matched with control

Information then collected on past exposure to a possible causal agent

75
Q

What is a cohort study?

A

Prospective

Participants selected on their exposure to a particular agent and followed up to see how many develop disease

76
Q

Cross-sectional study

A

‘snap shot’ to find prevalence

77
Q

What is the standardised mortality rate?

A

Observed deaths / expected deaths

78
Q

What does standardised mortality rate of 100 indicate?

A

Mortality in the group being studied is the same as the standard population

79
Q

What is the mortality rate?

A

Number of deaths in a particular population at a particular time

80
Q

What is the maternal mortality rate?

A

deaths linked to childbearing per live births per year

81
Q

What is the infant mortality rate?

A

Deaths <1 year per live births per year

82
Q

What is the fetal mortality rate?

A

Fetal deaths per live births per year

83
Q

What is external validity?

A

Degree to which the conclusions in the study would hold for other persons in other places at other times

e.g. ability to generalise

84
Q

What is internal validity?

A

How confident we are that the change in the independent variable caused the observed change in the dependent variable

85
Q

What is face validity?

A

Does it appear to test what it is meant to?

86
Q

What is content validity?

A

Extent to which a test or measure assesses the full content of a subject or area

87
Q

Methods of assessing validity in qualitative research

A

Triangulation

Respondant validation

Bracketing

Reflexivity

88
Q

What is triangulation in qualitative research?

A

Compares results from 2 or more different methods of data collection, or from 2 or more data sources

Used to assess validity

89
Q

What is respondant validation in qualitative research?

A

Investigators account is compared to those of research subjects

Used to assess validity

90
Q

What is bracketing in qualitative research?

A

Putting asides ones own beliefs / knowledge

91
Q

What is reflexivity in qualitative research?

A

Being sensitive to the ways the researcher and research process have shaped the collected data

92
Q

What is work up bias?

A

Clinicians reluctant to order gold standard test if new test is negaive

93
Q

What is expectation bias?

A

Observers subconsciously measure/ report data in a way that favours study outcome

94
Q

What is the Hawthorne effect?

A

group changes its behaviour because it is being watched

95
Q

What is procedure bias?

A

Subjects in different groups receive different treatments

96
Q

What is anchoring bias?

A

When the first piece of information influences decisions too much

97
Q

what is late-look bias?

A

Gathering information at an inappropriate time

98
Q

What is lead time bias?

A

New test diagnoses earlier but there is no effect on the outcome of the disease

99
Q

What is Berkinson’s/hospital bis?

A

Occurs in case control studies where hospitalised patients are used as controls

100
Q

How to calculate risk

A

number of events / number at risk

101
Q

how to calculate odds

A

number of events / number of non-events

102
Q

How to calculate relative risk (or risk ratio)

A

Risk in exposed group / risk in unexposed group

103
Q

How to calculate odds ratio

A

Odds of having been exposed / Odds in a control group

104
Q

What does correlation tell us?

A

How one variable may increase or decrease as another variable changes, but not by how much

105
Q

What does linear regression tell us?

A

How much one variable changes when a second variable is changed

106
Q

What is cost-effectiveness analysis?

A

Compares interventions by relating costs to a single clinical measure

combines costs and effects into an incremental cost-effectiveness ratio (ICER)

107
Q

What is cost-benefit analysis?

A

All costs and benefits are measured in terms of money

108
Q

What is cost-utility analysis?

A

Form of cost-effectiveness analysis but allows comparison between different diseases

Uses QALY

109
Q

What method of analysis uses QALY?

A

Cost-utility analysis

110
Q

What does 1 QALY equal?

A

1 year in perfect health

111
Q

What does QALY measure?

A

Gains in life expectancy and health related quality of life

can be negative

112
Q

What is cost-minimisation analysis?

A

Aim is to decide the least costly way of achieving the same outcome

AKT (20 decks)

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