Primer 14 - Biostats, Aplication Of Test Data

Question 1

What is incidence and what is the incidence equation?

Answer 1

Incidence is the new cases of diagnosis of a disease over a given period of time. Incidence = Total # of new cases in a period of time / Total # of individuals at risk of diagnosis in a period of time.

Question 2

In which type of studies can yield relative risk?

Answer 2

Cohort studies.

Question 3

In which type of studies yield odds ratio?

Answer 3

Case-control.

Question 4

What is the X and Y axis in a Odds ratio vs Relative risk ratio square?

Answer 4

X axis is the Disease (just like in diagnostic test) but Y axis is Risk factor (it is test results in diagnostic test).

Question 5

What is the equation of relative risk?

Answer 5

RR = [A/(A+B)]/[C/(C+D)]

A: Positive Risk factor with Positive for disease.
B: Positive Risk factor with Negative for disease.
C: Negative Risk factor with Positive disease.
D: Negative Risk factor with Negative for disease.

Question 6

What is the equation for Odds ratio?

Answer 6

OR: [A/B] / [C/D]

A: Positive Risk factor with Positive for disease.
B: Positive Risk factor with Negative for disease.
C: Negative Risk factor with Positive disease.
D: Negative Risk factor with Negative for disease.

Question 7

What happens to Relative risk when the disease prevalence is very low?

Answer 7

It approximates Odds ratio.

Question 8

What is attributable risk and what is the equation for it?

Answer 8

The risk of disease among exposed versus risk of disease to those not exposed.

AR: Incidence of disease (exposed) - Incidence of disease (unexposed).

Question 9

What is absolute risk reduction and what is its equation?

Answer 9

It is the reduction of risk of a disease after a certain intervention.

ARR: [C/(C+D)] - [A/(A+B)].

A: Positive intervention + Positive for disease.
B: Positive intervention + Negative for disease.
C: Negative intervention + Positive for disease.
D: Negative intervention + Negative for disease.

Question 10

What is Numbers Needed to Treat and the equation for it?

Answer 10

NNT is the number of patients you would need to treat in order to save/affect one life. It is NNT = 1/Absolute risk reduction.

Question 11

Why is NNT important?

Answer 11

To help determine if a drug is cost effective.

Question 12

What is the Number Needed to Harm and what is the equation for it?

Answer 12

It is the measurement of the extra risk that is due to an exposure. NNH: 1/Attributable risk.

Question 13

What is the absolute risk reduction and number needed to treat in the following example: In a study where 100 patients received medication Z to prevent the development of diabetes and 200 patients did not receive the medication, 10 patients in the experimental group developed diabetes and 40 patients in the control group developed diabetes.

Answer 13

A: Positive intervention & positive for disease = 10.
B: Positive intervention & negative for disease = 100-10= 90.
C: Negative intervention & positive for disease = 40.
D: Negative for intervention & negative for disease = 200-40= 160.

ARR: [C/(C+D)] - [A/(A+B)]: [40/200]-[10/100]: 0.2 - 0.1 = 0.1 = 10%.
NNT: 1/ARR= 1/0.1 = 10 = need to treat 10 patients to prevent 1 case of diabetes.

Question 14

What is precision and what is another name for it?

Answer 14

AKA reliability, it is a measure of how reproducible a result is; no random variation of results but does not reflect if the result being reproduced is the actual truth.

Question 15

What is accuracy and what is another name for it?

Answer 15

AKA, validity, a description of how closely a test results reflect the truth.

Question 16

The small town of Mickey City (pop. 8K) is immediately adjacent to factories where asbestos products are produced. During the past year, the prevalence of mesothelioma has been 16 cases. In the town of Donaldville (pop. 6K), 15 miles upwind of (and theoretically safely distant from) Mickey City, there was a prevalence of 3 cases during the same year. What is the relative risk of mesothelioma for the population of Mickey City?

Answer 16

RR: [A/(A+B)]/[C/(C+D)]

Question 17

What is prevalence and what is the prevalence equation?

Answer 17

Prevalence is the total number of people with the disease at a certain point in time. Total of people with a certain disease / Total population with or without the disease.
Also, Prevalence = Incidence x Disease duration.

Question 18

The small town of Mickey City (pop, 8K), is immediately adjacent to factories where asbestos products are produced. During the past year, the prevalence of mesothelioma has been 16 cases. In the town of Donaldville (pop, 6K) 15 miles upwind of (and safely distant from) Mickey City, there was a prevalence of 3 cases during the same year. What is the relative risk of mesothelioma for the population of Mickey City?

Answer 18

RR: [A/(A+B)] / [C/(C+D)].
We know that A= 16 and C= 3. We don’t know B or D but we know that A+B is the population of Mickey City and that C+D is the population of Donaldville.
Therefore, [16/8000] / [3/6000] = 4.
So the relative risk of mesothelioma is 4 times higher in Mickey City than Donaldville.

Question 19

A new glucose test arrives and you decide to see how well it works. There is a standard substance provided that has 90 mg/dL of glucose. Your repeated measurements of the substance reveal the following values: 54, 56, 55, 54, 53, 56, 55, and 54. What can you say about the precision and accuracy of your new glucose test?

Answer 19

Precision is good but accuracy is bad.

Question 20

The prevalence of varicella in population A is 2 times the prevalence of varicella in population B. The incidence is the same in population A and B. What can be assumed about the disease duration in population A versus population B?

Answer 20

Duration of varicella is twice as long in population A as in population B.