Types of Study and Risk Calculations

Question 1

Define prevalence

Answer 1

proportion of a particular population found to be affected by a medical condition at a specific time

Question 2

Define incidence

Answer 2

number of newly diagnosed cases in a particular time

Question 3

Describe a cross sectional study?

Answer 3

• This basically looks at a selected population in a moment in time
• It is good for looking at prevalence

Question 4

Describe a case control study?

Answer 4

this is retrospective (looks into the past)
* look at a group to see if they had a particular risk factor and outcome or exposed to a risk factor and if they get that outcome
* And then you look to see who was exposed or not exposed to a certain risk factor in both groups and compare

Question 5

Describe a cohort study?

Answer 5

this can be prospective or retrospective
* The study participants are chosen and compare those who have risk factors present versus those who don’t and see who has a particular outcome

Question 6

Absolute Risk calculation?

Answer 6

AR (absolute risk) = the number of events in treated or control groups, divided by the number of people in that group

You work out ARC for the control group and ART for the treatment group

Question 7

Absolute risk reduction calculation?

Answer 7

ARC – ART

Question 8

Relative risk?

Answer 8

ART / ARC

Question 9

Relative risk reduction?

Answer 9

(ARC – ART) / ARC

Question 10

Number needed to treat?

Answer 10

NNT (number needed to treat) = 1 / ARR

Question 11

Define sensitivity?

Answer 11

chance of you getting a positive result if you do have the disease
Sensitivity- how good is the test at detecting disease
= number of people with a positive result and the disease/ total number of people with the disease x 100

Question 12

Define specificity?

Answer 12

chance of you getting a negative result if you dont have the disease
Specificity – how good is the test at detecting those without the disease
= number of people who have a negative result and no disease/ number of people who do not have the disease x 100

Question 13

Positive predictive value?

Answer 13

chance you do have the disease if you have a positive result
Positive predictive value = how reliable is the test when it shows disease is present?
Number of people with a positive result and have the disease/ number of people with a positive test x 100

Question 14

Negative predictive value?

Answer 14

chance you dont have the disease if you have a negative result
Negative predictive value = how reliable is the test result when it shows disease is not present
Number of people who have a negative test result and no disease/ number of people with a negative test