statistics

Question 1

what is the mean

Answer 1

the average

Question 2

what is the mode

Answer 2

the most popular number

Question 3

what is the median

Answer 3

the middle number in a data set arranged from highest to lowest

Question 4

sensitivity - probability a test detects the disease if the disease is present

Answer 4

TP/TP+FN

Question 5

Sensitivity in terms of FN rate

Answer 5

1-FN rate

Question 6

Specificity probability that a test indicates non-disease when disease is absent

Answer 6

TN/TN + FP

Question 7

PPV

Answer 7

TP/TP + FP

Question 8

how does PPV vary with prevalence?

Answer 8

directly proportional

Question 9

How does NPV vary with prevalence

Answer 9

it is inversely proportional (lower the prevalence, higher the NPV or higher the prevelance of the disease, lower the NPV)

Question 10

PNV

Answer 10

TN/TN+FN

Question 11

Confounding

Answer 11

stratify there will be no significant difference in risk

Question 12

effect modification

Answer 12

stratify there will be a significant difference

Question 13

Examples of effect modication

Answer 13

• family hx and with OCP – risk of BC
• smoking and estrogen use – risk of VT
• smoking and asbestos – risk of lung cancer

Question 14

does disease prevalence effect sensitivity or specificity?

Answer 14

no

Question 15

OR

Answer 15

a/c /b/d or AD/BC

Question 16

RR

Answer 16

a/a+b /c/c+d

Question 17

attributable risk

Answer 17

difference in risk between the exposed and unexposed groups = a/a+b - c/c+d

Question 18

absolute risk reduction

Answer 18

difference between risk of case and control

Question 19

NNT = number of patients who need to e treated for 1 patient to benefit

Answer 19

1/absolute risk reduction

Question 20

NNH = number of patients who need to be exposed to the risk factor for 1 patient to be harmed

Answer 20

1/attributable risk

Question 21

positive skew

Answer 21

mean > median > mode , so mean is to the right

Question 22

negative skew

Answer 22

mean