Lecture 1-Clinical Prevention I Flashcards
List the 4 categories of Clinical Prevention Activities & what they mean.
- Screening Programs: Find disease early and treat it
- Vaccination: Working with the immune system to prevent disease
- Chemoprophylaxis: Drug therapy to prevent disease
- Behavioral Counseling Interventions: Change habits, lifestyles
List the 3 clinical prevention categories & what they mean.
- Primary prevention: Preventing disease BEFORE it occurs (treating risk factors)
- Secondary prevention (screening): Diagnosing disease early, before it causes symptoms
- Tertiary prevention: Preventing complications of (and mortality from) diagnosed, clinical disease
Describe the USPSTF grade of recommendations A - I.
A – good evidence for
B – fair evidence for
C – good vs. harm too close to call
D – fair evidence against
I – insufficient evidence to make recommendation
Is NPV or PPV most important for the 1) treatment, 2) clinical prevention, and 3) population oriented aspects of screening tests?
Negative predivtive value is the most important for treatment and clinical prevention aspects of screening tests. While positive predictive value is most important aspect for population oriented prevention.
What is the “Frame” Criteria for Screening Programs:
Disease is ______
Test is ______
Disease has early, ______ phase
Treatment ______
Treatment is ______
Treating early ______ morbidity and mortality
Disease is important
Test is accurate
Disease has early, asymptomatic phase
Treatment exists
Treatment is effective
Treating early reduces morbidity and mortality
The best way to study screening programs is via?
RCT’s
What is Lead Time Bias & how do we prevent it?
Lead time bias is when Screening falsely appears to extend life.
Screening can give you a jump on the disease (vs normal diagnosis time); this “lead-time” is a good thing, but it can bias the efficacy of screening. If two subjects have the same age, same time of disease onset, the same detectable pre-clinical phase, and the same time of death; the subject whose disease was identified through screening appears to survive longer, but only because their disease was identified earlier.
The way to prevent Lead Time Biasis to have a long enough follow up after a study of screened vs non-screened groups.
What is Length Time Bias & how do we prevent it?
Length Time Bias is when Screening over-represents less aggressive disease
There is a greater chance that screening will detect subjects with long detectable pre-clinical phase, and therefore, more benign disease. This is because more aggressive disease that will kill you faster, hence, screening does not “catch” it.
Way to prevent this is to decrease the time interval or have better test that will catch the more aggressive disease.
Describe selection bias.
Selection bias = improper randomization (non-randomization).
The people that sign up for screening tests are generally more healthy than people who do not sign up = internal validity component.
External validity component is that you are not testing a population representative of people who you treat (people who volunteer are not like the one you treat).
Describe overdiagnosis bias.
Researchers evaluating the program may be overzealous in diagnosing the disease and falsely conclude that the program is effective (because truly normal people are getting the preventive intervention).
You are diagnosing things that are not true disease or are a less aggressive disease. So if you include a bunch of people without disease you can overestimate the screening.
Describe refferal bias.
If screening programs are evaluated in tertiary care offices – prevalence/pre-test probability will be higher (more pathology in a tertiary care office). Prevalence/ pre test probability is generally lower in the primary care office and screening is done in the primary care setting.
Has to do also with the external validity portion of selection bias.
Describe a Proper Screening Program evaluation
RCT of screening vs. no screening with long follow-up and appropriate interval of screening and selection of patients.
