October 23

Question 1

What is primary prevention?

Answer 1

• maintenance of health through individual or community efforts so that the disease process never starts
• activites occur before pathological onset of the disease
• prevents disease from occurring; reduces incidence
• assume that the action taken will reduce the occurrence of disease and its after-effects
• ex: birth control, vaccines, healthy eating, exercise, sunscreen, seatbelt, not smoking, clean air/water, safe food

Question 2

What is secondary prevention?

Answer 2

• works to prevent the clinical symptoms after the onset of pathology
• reduces expression and severity of clinical disease
• do not prevent disease occurence but identify asymptomatic individuals during window between onset of pathology and symptoms
• delays onset of disease and improves survival
• decreases duration of remission, relapse, death
• ex: HIV screening (early use of antiretroviral drugs)
• involves screening or treating people to decrease duration

Question 3

What is tertiary prevention?

Answer 3

• helps people live with the disease
• goal is to improve survival by slowing/blocking progression of disease, reducing impairments and disabilities, improving quality of life/survival
• prompt treatment, follow-up, patient education, rehabilitation
• ex: drugs to prevent opportunistic infection in those with HIV infection reduce hospitalization and improve quality of life/survival, medical cannabis

Question 4

What is screening and how is it done?

Answer 4

• identifying asymptomatic healthy individuals who may be at increased risk disease or conditon
• use simple tests and try to identify people with risk factors/early stage of disease

Question 5

What are some important criteria for screening according to WHO?

Answer 5

• important health problem
• should be a treatment/something you can do about it
• if you start catching disease earlier, need money in healthcare system to pay for all these new patients

Question 6

How are screening programs evaluated through a non-randomized study?

Answer 6

• non-randomized studies (measure outcomes of people screened or not screened)
• problem is people are self selecting to be screened so they may be healthier/more compliant people than the general population
• this could lead to better outcomes but not be because of screening (volunteer bias)

Question 7

How are screening programs evaluated through an RCT?

Answer 7

• people are randomly selected to be part of the screened or not screened arms
• problems: long follow up, very expensive
• unintended crossovers: people may choose to get screened in the “not screened” arm, people might not be able to be in the arm that they are assigned to (analyzed on intent to treat so can have contamination)

Question 8

What is lead time?

Answer 8

• lead time is the extra time between screen-diagnosed disease and diagnosis based on clinical symptoms
• how much sooner does the screening tell you about the disease than your symptoms?

Question 9

What conditions are screening tests useful for?

Answer 9

-inherited conditions

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Question 10

What is lead time bias?

Answer 10

• because of extra lead time in people who are screened, survival after diagnosis appears to be longer than for those who are not screened
• can happen because you find a subclinical disease; disease does not progress so finding it earlier doesn’t make a difference
• could also be that there are no treatments that can improve their survival
• better to measure how many people survived at a given time after screening or not screening

Question 11

In RCT looking at screening versus not screening for prostate cancer, why were there more deaths in screening group with more cases diagnosed?

Answer 11

• treatment might not have been effective
• by getting diagnosed, led to increased fatality (maybe all of the treatments you got led to dying earlier)
• screening didn’t work (probably isn’t the case because we saw more were diagnosed)
• overdiagnosis; maybe we found the ones who wouldn’t have died from it
• not enough follow up (not enough time to see difference between screening arm and non screening arm)
• changes in cancer therapy over time (could have been that catching the cancer late was still fine because of better treatments)

Question 12

What can account for the differences in the PLCO and ERSPC?

Answer 12

• ERSPC screening interval was 2-4 years so it could have been that here you were catching less insignificant cancers and getting the ones that needed to be treated
• most men in PLCO were screened for PSA so maybe you can’t actually see the difference because most of them were screened

Question 13

How is the validity of a test evaluated?

Answer 13

1. How many people are correctly diagnosed with the disease? (TRUE POSITIVE)
2. How many people are correctly diagnosed without the disease? (TRUE NEGATIVE)
3. How many people are misdiagnosed with the disease but do not have it (with new test)? (FALSE POSITIVE)
4. How many people are misdiagnosed without the disease but do have it (with new test)? (FALSE NEGATIVE)

Question 14

What is sensitivity?

Answer 14

-ability of the test to correctly identify who has the disease (denominator is all people with the disease)

TP/(TP+FN)

Question 15

What is specificity?

Answer 15

-ability of the test to correctly identify who does NOT have the disease (denominator is all people without the disease)

TN/(FP+TN)