Talking about risk Flashcards
Arguments for using PSA as a screening test for prostate cancer?
- May reassure you if the tests are normal
- It can find early signs of cancer meaning you can get treated early.
- PSA testing may reduce the risk of dying if you do have cancer
Arguments against using PSA for prostate cancer?
- Does not detect all prostate cancer so might provide false reassurance
- Raised PSA can also be a sign of enlarged prostate, prostatitis, urinary infection so might unnecessarily worry the patient
- About 3/4 men with raised PSA will NOT have cancer so it could lead to unnecessary worry and tests
- Can’t differentiate between slow growing and fast growing cancers
- Might detect a slow growing cancer which will worry the patient even though it likely would have never caused any problems
- Cost £0.8bn per year for screening
What is the difference between relative risk and absolute risk?
Relative risk - A measure of the risk of a certain event happening in one group compared to the risk of the same event happening in another group.
Absolute risk - the change in the risk of an outcome of a given treatment in comparison to another treatment
What is the number needed to treat?
Average number of patients who need to be treated to see a benefit in one patient.
What is illusion uncertainty?
Illusion of certainty - thinking 20% reduction in risk means risk goes down from 20% to 0%.
A randomised controlled trial is performed to look at a new drug to prevent hip fractures in postmenopausal women. Group A consists of 1,000 women who take the new drug whilst group B contains 1,400 women taking a placebo. The hip fracture rate in group A is 2% and in group B is 4%. What is the number needed to treat to prevent one hip fracture?
They key to answering this question is to ignore irrelevant data such as the number of patients in each group.
Control event rate = 4% = 0.04
Experimental event rate = 2% = 0.02
Absolute risk reduction = 0.04 - 0.02 = 0.02
Number needed to treat = 1 / 0.02 = 50
