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Primary FRCA MCQ > Statistics > Flashcards

Statistics Flashcards

1
Q

How do you calculate Absolute Risk Reduction (ARR)

A

ARR = Control rate - experimental rate

(If a control has a risk of PONV 20/100 compared to an experimental drug 10/100 the ARR = 0.2 - 0.1)

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2
Q

How do you calculate Number Needed To Treat (NNT)

A

1/ARR

(Absolute risk reduction)

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3
Q

How do you calculate Relative Risk (RR)

A

RR = Experimental event rate / Control event rate

(If a control has risk of PONV 20/100 and experimental drug has risk 10/100 RR= 0.1/0.2)

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4
Q

What type of error is a false positive

A

Type 1 error (alpha)

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5
Q

What type of error is a false negative

A

Type 2 error (Beta)

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6
Q

How do you calculate power of a study

A

Power = 1 - Beta (Type 2 error)

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7
Q

Which statistical test can be used for comparing 2 sets of continuous normally distributed (parametric) data

A

T-test

Paired if the same subject is in the control group and also in the experimental group

otherwise unpaired

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8
Q

Which statistical test can be used for comparing more than 2 sets of continuous normally distributed (parametric) data

A

ANOVA test

(Can do multiple t-tests but higher risks of error)

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9
Q

What percentage of a population lies within 1 standard deviation (SD) from the mean

A

68%

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10
Q

What percentage of a population lies within 2 standard deviations (SD) from the mean

A

95%

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11
Q

What percentage of a population lies within 3 standard deviations (SD) from the mean

A

99.7%

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12
Q

How does the size of the difference you’re looking for between 2 groups affect power

A

Small difference = low power

High Beta error ( false negative)

Needs high n number

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13
Q

How does the SD affect power

A

Large SD = large area = low power

high Beta error

Needs high n Number

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14
Q

How does the p value affect power

A

low p value = high confidence can reject null hypothesis = low power

High Beta error

Needs high n number

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15
Q

How does parametric vs non-parametric test affect power

A

Non-parametric = low power

high beta error

Needs high n number

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16
Q

How do you calculate standard error of the mean

A

SD/ √n

standard deviation/ square root of sample size

17
Q

How does standard error of the mean give you 95% CI

A

95% confidence interval is 2 standard errors of the mean above and below.

18
Q

How do you calculate variance

A

Σ(x-x̄)²/ n-1

the difference of each value from the mean added together and squared then divided by the sample size -1 (degree of freedom)

19
Q

How do you calculate standard deviation from variance

A

SD = √variance

= √Σ(x-x̄)²/ n-1

20
Q

What does it mean if the 95% confidence intervals of 2 groups do not overlap

A

There is likely to be a significant statistical difference

21
Q

Which statistical test can be used for comparing more than 2 groups of quantitative non-parametric data

A

Kruskal wallis test

22
Q

Which 2 statistical tests can be used for comparing 2 groups of quantitative non-parametric data

A

Mann Whitney

Wilcoxian

23
Q

Which parameter is used to look at the central tendency of non-parametric data

A

Median

(use median instead of mean)

24
Q

Which parameter is used to look at the central tendency of parametric data

A

Mean

25
Q

Which parameters are used to look at spread of non-parametric data

A

Range
Inter quartile range (from start of Q2 (25%) to end of Q3 (75%) )

26
Q

Which 2 statistical tests can be used for comparing 2 groups of qualitative data

A

Fisher’s exact test
Chi- Squared test

27
Q

What does a correlation coefficient of r = +1 mean

A

perfect positive linear correlation. All data points lie exactly on a straight line with +ve gradient

28
Q

What does a correlation coefficient of r = -1 mean

A

perfect negative linear correlation. All data points lie exactly on a straight line with -ve gradient

29
Q

What does a correlation coefficient of r = 0 mean

A

No linear correlation between data points

30
Q

When would you use Pearson’s correlation coefficient

A

When comparing 2 groups of parametric data to look for degree of correlation with linear relationship

31
Q

When would you use Spearmen’s rho correlation coefficient

A

When comparing 2 groups of which at least 1 has non- parametric data to look for degree of correlation with linear relationship

32
Q

Define what is meant by co-efficient of determination (r²)

A

(This is correlation co-efficient squared)

The proportion of the variation (variance) in the dependent variable that is predictable from the independent variable

e.g r ² of 0.64 means that 64% of the variance in y is predictable from the variance in x

33
Q

What is the Bland-Altman plot used for

A

Used to compare 2 different measuring devices

X-axis: Both measurement device results added together and divided by 2 (average) (the true value)

Y-axis: Difference between the values measured by each device

34
Q

How do you calculate Relative Risk Reduction (RRR)

A

RRR = (Control event rate - Experimental event rate) / Control event rate

(If a control has risk of PONV 20/100 and experimental drug has risk 10/100

RRR= (0.2 - 0.1)/0.2

35
Q

When would you use odds ratio (OR) instead or relative risk (RR)

A

Case control studies

RR can only be used in cohort studies whereas OR can also be used in cohort and case control

36
Q

What does an odds ratio (OR) of 1 mean

A

There is no association between exposure to the treatment and improved outcomes

Null hypothesis

37
Q

What does an odds ratio (OR) < 1 mean

A

There is a negative association

The odds of an event happening in the exposed/treated group is less than the control group

(e.g treatment reduces odds of stroke)

38
Q

What does an odds ratio (OR) > 1 mean

A

There is a positive association

The odds of an event happening in the exposed/treated group is higher than the control group

(e.g treatment increases odds of stroke)

Primary FRCA MCQ (6 decks)

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