Statistics

Question 1

Sensitivity calculation

Answer 1

True positives/number of people with disease

Question 2

Specificity calculation

Answer 2

True negatives/number of people without the disease

Question 3

Positive predictive value calculation

Answer 3

True positives/all positives

Question 4

Negative predictive value calculation

Answer 4

True negatives/all negatives

Question 5

Positive likelihood ratio calculation

Answer 5

Sensitivity/(1-specificity)

Question 6

Negative likelihood ratio calculation

Answer 6

(1-sensitivity)/specificity

Question 7

Variance calculation

Answer 7

(Value - mean) squared for each value and sum them
Divide by n-1

Question 8

SD calculation

Answer 8

Square root of variance

Question 9

What percentage of data is within 1 SD of mean?

Answer 9

68%

Question 10

What percentage of data is within 2 SDs of mean?

Answer 10

95%

Question 11

What percentage of data is within 3 SDs of mean?

Answer 11

99.7%

Question 12

What is the coefficient of variation?

Answer 12

SD as a percentage of the mean

SD / mean x 100

Question 13

SEM calculation

Answer 13

SD / square root of n
or
square root of SD squared / n

Question 14

How do you normalise skewed data?

Answer 14

Take the log, square root, square, or reciprocal (1/x)

Question 15

95% CI calculation

Answer 15

+/- SEM x 1.96

Question 16

Calculation of SD in binomial sample

Answer 16

p = proportion e.g. 40%
p x (1-p)

Question 17

Calculation of SEM in binomial sample

Answer 17

square root of: p x (1-p) / n

Question 18

What is Poisson distribution?

Answer 18

Number of occurrences of an events per unit of time (distribution of discrete data)
Variance = mean

Question 19

SD calculation for Poisson distribution?

Answer 19

Squre root of mean
(mean = variance)

Question 20

Types of data

Answer 20

Nominal - naming scale e.g. eye colour
Ordinal - ordered values e.g. first, second, third
Discrete - integers
Continues - can be non-whole numbers
Interval - distance between values is the same and can be +ve or -ve e.g. 1, 2 ,3 or 5, 10, 15
Ratio - interval scale with fixed 0 e.g. height, weight

Question 21

Statistical test for correlation between two variables

Answer 21

Normal - Pearson’s coefficient
Non-normal - Spearman’s ranked coefficient

Question 23

Z score calculation?

Answer 23

(Value - mean) / SD

Question 24

Maternal mortality ratio

Answer 24

Maternal deaths per 100,000 live births in a year
(8.2 in UK in 2008)

Question 25

Maternal mortality rate

Answer 25

Maternal deaths per 1000 women of reproductive age

Question 26

Perinatal mortality rate

Answer 26

Number of stillbirths and deaths in first week of life per 1000 live births
(8 in 1000 in UK)

Question 27

Perinatal mortality rate

Answer 27

Number of stillbirths from 22/40 and deaths in first week of life per 1000 live births
(8 in 1000 in UK)