Statistics

Question 1

Symmetrical vs asymmetrical data

Answer 1

Positive skew, to the left of graph

Symmetrical is when graph peaks in the middle and slopes on either side

Question 2

When to use mean

Answer 2

Symmetrical data

Question 3

When to use median

Answer 3

Asymmetrical data, outliers in data

Question 4

When to use mode

Answer 4

Nominal data

Question 5

Why is range avoided as a statistical aide

Answer 5

Too simple, extreme scores cause problems

Question 6

What is interquartile range

Answer 6

Middle 50%, from 25 to 75th percentile. Used for skewed data to measure the spread

Question 7

Problem with interquartile range

Answer 7

Ignores 50% of scores

Question 8

When is standard deviation and variance used

Answer 8

Shows spread of data around mean, symmetrical data

Question 9

Relation between standard deviation and variance

Answer 9

Standard deviation = Square root (Variance)

Question 10

Calculating variance

Answer 10

Sum of (Individual date - Mean) / Number of obs

Question 11

What are confidence intervals

Answer 11

Ascertaining potential variability around an estimate

Question 12

What if the in between group difference lies in confidence interval

Answer 12

Result is significant

Question 13

Is this result significant?
At 60 h, mean reduction in total score was 21.0 points in the brexanolone group compared with 8.8 points in the placebo group (difference -12.2, 95% CI -20.77 to -3.67)

Answer 13

Yes

Question 14

Is this result significant?
Proportion of patients achieving a global response … was 56.3% with brentuximab vendotin versus 12.5% with physician’s choice, resulting in a between-group difference of 43.8% (95% CI 29.1 – 58.4)

Answer 14

Yes

Question 15

At 6 months, 285 (47%) of 607 patients and 287 (47%) of 605 controls were dead or dependent (odds ratio 0.98, 95% CI 0.78-1.23). Is this significant?

Answer 15

No as the confidence interval crosses 1.

Question 16

What values for difference, odds ratio, hazard ratio and risk ratio show no difference

Answer 16

Difference = 0, Odds ratio, Hazard ratio and Risk ratio = 1

Question 17

Are the following significant?

1. Hazard ratio - 2.06 - 0.88 – 4.82
2. Difference - 4.58 - 0.85-7.89
3. Odds ratio - 0.21 - 0.08-0.55
4. Adjusted mean difference - 0.36 - 0.21-0.52
5. Odds ratio - 1.20 - 0.59-2.44
6. Risk ratio - 1.47 - 0.10-1.98

Answer 17

1. Insignificant value for hazard is 1 and CI crosses this
2. Significant as CI doesn’t cross 0
3. Significant
4. Significant
5. Insignificant as CI crosses 1, value for odds ratio is 1
6. Significant

Question 18

What is the null hypothesis

Answer 18

The hypothesis that data from a control or placebo is due to change and there’s no difference in the groups. Ex, if testing for a new drug, null hypothesis is that the drug has no effect. We can also come up with an alternative hypothesis, the changes we see are due to the drug having an effect. The null hypothesis holds true unless proven otherwise

Question 19

What is the p-value

Answer 19

Probability value, probability of observed result given null hypothesis is true. Very low p-value can prove the null hypothesis to be false

Question 20

For what p-values is the evidence against null hypothesis weak, strong and very strong

Answer 20

p-value < 0.1 = Weak evidence against null hypothesis
p-value < 0.05 = Strong evidence
p-value < 0.01 = Very strong evidence

Question 21

200 adults seeing an asthma nurse speciailist were randomly assigned to either a new type of bronchodilator or placebo. After 3 months the peak flow rates in the treatment group had increased by a mean of 96 l/min and in the placebo group by 70 l/min.
The statistical test is conducted and a p-value of 0.001 obtained. What does this mean?

Answer 21

The p-value < 0.001 hence the result is significant as there’s strong evidence against the null hypothesis