Preventative Medicine Flashcards
What are the 3 categories of prevention?
Primary - preventing onset of disease e.g. immunisation
Secondary - halt progression of disease e.g. early diagnosis/screening
Tertiary - limit disability/complications in established disease e.g. rehabilitation
Describe: Geoffrey Rose’s single population theory
- Population-wide prevention - shift the mean of the entire distribution to the left to accommodate for the low-risk people
- Identify + treat the top end of the population distribution
Describe Geoffrey Rose’s single population theory with the example of preventing MIs
- Shift the distribution to the left to reduce everyone’s blood pressure - do this by reducing obesity and salt in diet
- Target the high-risk subjects - screening in GPs
Describe: individual-based intervention
- Identify individuals at high risk with screening
- Intervene only in individuals at high risk
- Risk-benefit balance assessed individually
Describe: population-based intervention
- Identify important risk factors for the community (prevalence)
- Policy to reduce risk factor irrespective of individual risk
- Risk-benefit balance for whole community
Define: sensitivity
The proportion of people with the disease who are identified as having it by a positive test
= a/(a+c)
Define: specificity
The proportion of people without the disease who are correctly re-assured by a negative test result
= d/(d+b)
Define: positive predictive value
The probability that a person with a positive test result actually has the disease
= a/(a+b)
Define: negative predictive value
The probability that a person with a negative test result doesn’t have the disease
= d/(c+d)
Describe: high sensitivity
- Maximises identification of diseased people in the screened population
- Relatively few false negatives
- Unnecessary investigations/treatments for others
- Lots of false positives
Why would high sensitivity be desirable?
- Adverse consequences of missed diagnosis for the individual might be significantly worse than early diagnosis
- Serious communicable diseases in society
- Correct diagnosis given before treatment started
Describe: high specificity
- Detects only people with the disease
- Relatively few false positives
- Will miss some people who have/are at risk of disease
- Lots of false negatives
Why would high specificity be desirable?
- Diagnosis is associated with anxiety/stigma
- Further investigations are time-consuming/painful
- Cases are likely to be detected by other means before it is ‘too late’ for effective treatment
- Treatment is to be offered without further investigations
Define: lead time bias
Early diagnosis falsely appears to prolong survival
In reality, it only identifies the disease early rather than increasing survival
Define: length time bias
Screening over-represents less aggressive disease (people with more severe miss the screening may be through death)
This makes the screening look better
What are the 10 principles for screening for disease laid out by Wilson and Jungner?
- The condition sought should be an important problem
- There should be an acceptable treatment for patients with the recognised disease
- Facilities for diagnosis and treatment should be available
- There should be a recognised latent or early symptomatic stage
- The natural history of the condition should be adequately understood
- There should be a suitable test or examination
- The test or examination should be acceptable to the population
- There should be agreed policy on whom to treat as patients
- The cost of case-finding should be economically balanced in relation to the possible expenditure
- Case finding should a continuous process and not a ‘once and for all’ project
Define: case fatality rate
Number of people who die from the disease/number of people with disease
Define: mortality rate
Number of people who die from disease/number of people who die
Define: risk
Number of new cases/number at risk
Relative risk = 1
The risk in the exposed group is the same as the risk in the unexposed group
Relative risk < 1
The exposure is associated with a protective effect
Relative risk > 1
The exposure is associated with harm
Define: odds ratio
(Those with the disease and exposed to risk factor x Those without disease and not exposed) / (Those with the disease and not exposed x Those without the disease and exposed)
Odds ratio = 1
The probability of an event occurring is the same as the probability that the event does not occur
What qualities must a hypothesis have?
- Plausible
- Falsifiable (able to be accepted/rejected)
- Have direction
- Be precise
