Statistics

Question 1

Variance =

Answer 1

Variance = SD squared

Question 2

Standard Error =

Answer 2

SD / Square root (n)

Question 3

Positive skew - highest to lowest mean median mode

Answer 3

Positive skew, Mean > Median > Mode

Question 4

Negative skew

Answer 4

Mode > Median > Mean.

The skew pulls the mean and median in its direction.

The mode is the least changed by skew.

Question 5

Normal distribution

Answer 5

Mean = Median = Mode

Question 6

Type 1 error

Answer 6

rejecting a correct null hypothesis,

false positive error

Question 7

Type 2 error

Answer 7

not rejecting an incorrect null hypothesis.

Question 8

Attributable risk

Answer 8

AR = a/(a+b) - c/(c+d)

AR = Prevalence of disease in the exposed group - prevalence of the disease in the non-exposed

Question 9

Absolute risk reducion

Answer 9

The reverse of the attributable risk.

ARR = c/(c+d) - a/(a+b)

Percentage of people who got the disease with no intervention - the percentage of people who got the disease after the treatment.

Question 10

Number needed to treat

Answer 10

NNT = 1/ARR

Pirates love treats ARR!

Question 11

Number needed to harm

Answer 11

NNR = 1/AR

hARm
1/AR

Question 12

LR+, positive likelihood ratio

Answer 12

LR+ = sensitivity/1-specificity = true positive % / false positive %

Question 13

LR-, neg LR ratio

Answer 13

= 1 - sensitivity / specificity = False negative rate / True negative rate