Epidemiology

Question 1

Assuming a normal distribution, what percentage of the population falls within:
1σ of the mean?
2σ of the mean?
3σ of the mean?

Answer 1

68%
95%
99.7%

Question 2

Assuming a normal distribution, what percentage of the population would be expected to lie at or above:
1σ from the mean?
2σ from the mean?
3σ from the mean?

Answer 2

16%

2. 5%
3. 15%

Question 3

What is β?

Answer 3

The chance of concluding there is no difference when there actually is one.

Question 4

Define power.

Answer 4

power = 1 - β

Question 5

What is type I error?

Answer 5

The chance of concluding there is a difference when there is none. (a.k.a. α).

Question 6

Formula for number needed to harm (NNH)

Answer 6

1/absolute risk increase

Question 7

How do we calculate absolute risk increase?

Answer 7

risk in tx grp - risk in control group

Question 8

calculate the number needed to harm if:

80% in treated group die and 60% in untreated group die.

Answer 8

1/(0.80-0.60) = 1/0.20 = 5

Question 9

calculate number needed to treat if:
Tx grp: 2 die, 3 live
control: 3 die, 1 lives

Answer 9

3/5 = 0.60 1/4 = 0.25
0.60 - 0.25 = 0.35
1/0.35 = ~3