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HSPH > Calculations > Flashcards

Calculations Flashcards

1
Q

RCT

How do you calculate relative risk of a treatment group [1] and control group? [1]

A
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2
Q

RCT

How do you calculate Relative Risk (RR) of death in treatment group compared to the control group? [1]

A
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3
Q

Calculate the relative risk Relative Risk (RR) of IQ≤85 treatment group compared to the control group using this data

A
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4
Q

Calculate the relative risk using this data

A

To calculate the risk in each group, we divide the number of people who died of AIDS by the population totals in each group

This gives us a risk of 0.0001919 among African Americans (50 divided by 260,553), and a risk of 0.0000198 among people from other race/ethnic groups (51 divided by 2,585,448).

To calculate the relative risk, we divide the risk among African Americans by the risk among people from other race/ethnic groups. This gives us a relative risk of 9.7
(0.0001919 divided by 0.0000198).

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5
Q

What does a relative risk of 9.7 mean for African Americans dying of AIDs? [1]

A

From this example, we can say that African
Americans are ten times as likely to die
from AIDS compared to people from other
race/ethnic groups (RR=9.7).

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6
Q

Interpet what it means if the relative risk of Group A is 0.8 [1]

A

If the relative risk were 0.8, people in
Group A would be 20% less likely than
people in all other groups to die from a
cause.

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7
Q

A researcher found that 20% of mice exposed to compound FC420 developed cancer and only 1% of mice not exposed to compound FC420 developed cancer. Which of the following is the best interpretation of these results?

A. One must know how many mice were tested to draw any conclusions
B. The odds of not developing cancer in the mice is 1:20
C. Mice exposed to FC420 have 20 times the relative risk of developing cancer
D. There is a 20% increase in the absolute risk of mice developing cancer when exposed to FC420

A

C. Mice exposed to FC420 have 20 times the relative risk of developing cancer

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8
Q

Calculate the relative risk of back injury associated with back belt use?

A

Risk of back injury among the workers who used back belts: 502/2939 = 0.1708
Risk of back injury among the workers who did not use back belts: 455 / 12601 = 0.1749
Relative risk: .1708 1.1749 = 0.98

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9
Q

Calculate the relative risk associated with exposure

A
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10
Q

Calculate the relative risk associated \vith the exposure within subgroup 1.

A

1.244

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11
Q

(f) Calculate the relative risk associated with the exposure within subgroup 2.

A

0.993

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12
Q

Calculate the relative risk of death in treated group compared to control group

A
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13
Q

Relative risk of NTD in folic acid group compared to placebo group

A
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14
Q

NNT

Calculate and interpret this question

“We conducted a randomized trial to test the efficacy of SuperMed. There were 2 groups: a group treated with SuperMed and a group treated with placebo. 100 patients in each.

In the group treated with SuperMed, 75% patients were still alive after a 1-year course. In the group treated with placebo, only 25% patients survived”.

A

NNT = 1/Absolute Rate of Risk
= 100 / (75-25)
= 100 / 50
NNT = 2

NNT means that for every two patients, SuperMed prevents one additional death, in comparison to placebo.

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15
Q

A randomised placebo controlled trial of a new treatment showed that the risk of death in the new treatment group was 5% and the risk of death in the placebo group was 10%.

What is the number needed to treat with the new treatment to prevent one death?

A

20
Tick (20 people, 20, 20%)

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16
Q

Cohort study

What is the relative risk of heart disease amongst heavy smokers compared to non smokers ?

A

1111 / 619 = 1.8

17
Q

Calculate the absolute excess risk of this data

A
18
Q

Calculate the odds ratio of this data

A
19
Q

Calculate the odds ratio for no sports participation and lumbar disk disease within
smokers. Include a brief interpretation.

A

Odds ratio: Odds in Case / Odds in Control

Odds in case: 36/138 = 0.26
Ods in control: 28 / 113 = 0.24

Odds ratio: 0.26/0.24= 1.08

Sports participation has little or no observable effect.

20
Q

(c) Calculate the odds ratio within non-smokers.

Iclude a brief interpretation. [2]

A

Odds ratio: Odds in Case / Odds in Control

Odds in case: 31/82 = 0.378
Ods in control: 20 / 126 = 0.158

Odds ratio: 0.378/ 0.158 = 2.38

No sports participation more than doubles in risk of lumbar disk disease.

21
Q
A

Odds ratio: Odds in Case / Odds in Control

Odds in case: 9/22 = 0.4
Odds in control: 247/432 = 0.57

Odds ratio: 0.4/0.57 = 0.72

22
Q

If the OR is 0.72, does ZDV appear to be effective in preventing HIV following needle stick injuries? [1]

A

Yes. The risk of HIV is decreased by - 28% with use of ZDV.

23
Q

A randomised placebo controlled trial of a new treatment showed that the risk of death in the new treatment group was 5% and the risk of death in the placebo group was 10%.

What is the number needed to treat with the new treatment to prevent one death?

A

20
Tick (20 people, 20, 20%)

24
Q

A non-randomised study looking at the association between preventive percutaneous coronary intervention (PCI) versus infarct artery only PCI in patients with ST elevated myocardial infarction was carried out. It found that in 280 patients receiving preventive PCI, 80 died after 5 years of follow-up. Of 120 patients receiving infarct artery only PCI 20 died after 5 years of follow-up.

Calculate the odds ratio of death in the preventive PCI group compared with the infarct artery only PCI group. Show your calculations.

A

PPCI (case): total =280; died = 80
IPCI (control): total = 120; died = 20

Odds of preventive PCI in patients that died = 80/20 = 4
Odds of preventive PCI in those that did not die = 200/100 = 2
Odds ratio = 4/2 = 2

25
Q

How do you calculate absolute excess risk from case control study? [1] Use example below:

Babies put on their sides are twice as likely to die rather than babies put on their backs.

From ONS: Population risk of SIDs = 3.4 per 10,000 per year

A

Can’t use risk because dont have risk values.

Therefore estimate of risk in babies put on their sides
= 2 x 3.4 per 10,000 per year
= 6.8 per 10,000 per year

estimate of absolute excess risk in babies put on their sides =
6.8 per 10,000 per year – 3.4 per 10,000 per year
= 3.4 per 10,000 per year

HSPH (9 decks)

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