practising public health definition Flashcards
Absolute risk reduction
The difference in the rate of adverse events in exposed and unexposed groups. This is mathematically identical to the attributable risk for a risk factor. (cf relative risk reduction and preventable fraction)
Suppose the risk of a deep vein thrombosis reduces from 0.03% to 0.02% following stopping the oral contraceptive pill; the absolute risk reduction is 0.01%, or 1 in 10,000.
Accuracy
The closeness of a measured value to a standard or known value. (cf precision)
The measurements of blood pressure in a patient by 10 different students were very precise as there was little variation in the results. However, all the readings were about 10 mmHg greater than the true blood pressure due to an inaccurate sphygmomanometer.
Attack rate
The proportion of those individuals who are at risk of an infectious disease who become clinically ill in a given time period (usually expressed as a percentage).
In an outbreak of food poisoning, out of 1000 diners there were 50 cases of diarrhoea within a week of the meal. The attack rate was 50 out of 1000 diners, or 5% of diners were affected.
Attributable fraction
The proportion of an outcome in people exposed that is due entirely to the risk factor (the attributable risk divided by the risk in the exposed population). (cf preventable fraction and relative risk reduction)
If smokers have a 25.2% lifetime risk of lung cancer and non-smokers a 0.2% lifetime risk, the attributable fraction is (25.2% − 0.2% = 25% divided by the risk in the exposed population (25.2%) = 0.99 (99%), or 99 out of 100 lung cancers in smokers are due to smoking.
Attributable risk
The difference in the rate of disease in the exposed group as compared to the unexposed group. This is mathematically identical to the absolute risk reduction for the effect of a treatment.
If smokers have a 25.2% lifetime risk of lung cancer and non-smokers a 0.2% lifetime risk, the risk of lung cancer in smokers that is attributable to, or caused by, their smoking is 25.2% − 0.2% = 25%.
Basic reproduction number (R0)
The average number of individuals directly infected by an infectious case during the entire infectious period when entering a totally susceptible population. (cf effective reproductive number and secondary attack rate)
If the basic reproduction number (R0) of measles is 12, each case of measles introduced into a non-immune population would result in the infection of 12 other people.
Clinically significant
An effect that is large enough that it is worth treating a patient. (cf statistically significant)
A new blood pressure drug reduces diastolic blood pressure by 0.001 mmHg. Although the result from the trial was statistically significant, the effect is not clinically significant because it is so small and does not warrant widespread use of the drug (which may have negative clinical consequences like side effects).
Confidence interval (CI)
calculated interval with a given probability (usually 95%) that the true value of the effect lies within the interval.
Suppose the increased risk of lung cancer from radon exposure is 20% and the 95% confidence interval is 16%–24%. Therefore we can be 95% confident that the true increased risk lies between 16% and 24%, and conversely, there is a 5% (or 1 in 20) chance that the true risk lies outside this range.
Confounding variable
factor that is independently associated with the exposure and outcome/ disease under study, but is not an intermediate factor between exposure and outcome.
People who eat more fruits and vegetables are less likely to be obese. However, this observation may be confounded (or explained either completely or partly) by people who eat more fruits and vegetables also being more likely to take exercise, which is independently related to obesity.
Cost-benefit analysis
formal comparison of the costs and outcomes of alternative interventions of which the costs and effects are not equal and results are expressed in terms of net benefit. Both costs and outcomes are measured in monetary units.
The cost-benefit analysis estimates that through savings over the next 20 years, investing £5 million in new road surfaces would benefit the economy by £10 million, compared to a £15 million benefit from investing £5 million in recruiting more nurses.
Cost- effectiveness analysis
formal comparison of the costs and outcomes of alternative interventions of which the costs and consequences are not equal and the results are expressed in terms of cost per unit of outcome. Outcomes are measured in natural units.
When comparing two blood pressure- lowering drugs, the cost-effectiveness analysis shows that drug A costs £5 per mmHg reduction in systolic blood pressure, compared to £4 per mmHg reduction for drug B.
Cost- minimisation analysis
Compares the costs of alternative interventions that are assumed to have an equivalent effect. The goal is to find the least costly alternative.
Using a cost-minimisation analysis, nurse- led endoscopy units may have been shown to cost £60 more per patient than doctor-led units.
Cost-utility analysis
A formal comparison of the costs and outcomes of alternative interventions of which the costs and consequences are not equal and the results are expressed in terms of cost per unit of outcome. Outcomes are usually measured in quality-adjusted life years (QALYs).
Per patient, the benefit (in terms of gain in quality-adjusted life years) from repairing a ruptured abdominal aortic aneurysm is significantly greater than prescribing a walking stick for recurrent falls (that also has a health benefit). However, the cost per QALY is much greater for the abdominal aortic aneurysm repair, as for the price of one operation you could buy more than 1000 walking sticks.
Cumulative incidence
See risk.
Effective (net) reproductive number
The average number of individuals directly infected by an infectious case during the entire infectious period when entering a typical population of susceptible and non-susceptible individuals. (cf basic reproduction number and secondary attack rate)
Each case of measles (R0 = 12) introduced into a population half of whom were immune to measures would result in the infection of six other people.
Endemic
The maintenance of a disease or illness in a community or region without the need for external inputs.
Herpes simplex virus is endemic to the UK; it does not require any external increase in cases to be maintained. This compares to malaria, which can be acquired in the UK in some exceptional scenarios but is not maintained due to lack of vector.
Epidemic
The occurrence in a community or region of cases of a disease or illness clearly in excess of normal expectancy.
A ‘flu epidemic is declared when the number of cases identified is greater than what would be expected under usual circumstances.
Evidence-based medicine
The ability to access, summarise and apply information from the literature to day-to-day clinical problems.
Evidence-based medicine is decision making based on sound scientific study rather than on the opinion of one or more individuals.
False negative
Test result is negative but the person has the disease (i.e. test result is incorrect).
A test result that indicates no disease but in fact the person does have the disease.
False positive
Test result is positive but the person does not have the disease (i.e. test result is incorrect).
A test result that indicates disease but in fact the person does not have the disease.
Gross domestic product
(GDP)
GDP measures total output within the geographical boundaries of the country, regardless of the nationality of the entities producing the output.
In 2012, the GDP of the United States was $16,250 billion and for Monaco $6 billion. The GDP per capita, however, was $160,000 for Monaco and $50,000 for the United States.
Hazard
A source of potential damage, harm or adverse health effects (cf risk).
The danger associated with something.
Herd immunity threshold
The proportion of the population who need to be immune to put transmission in decline.
Once 95% of children are vaccinated against measles, the disease no longer has a large enough susceptible population in which to sustain replication and case numbers will then decline.
Incremental cost- effectiveness ratio (ICER)
The ICER is obtained by dividing the cost differences (C1 – C2) by the outcome differences (E1 – E2) for an intervention where C1 and E1 are cost and effect of the intervention, and C2 and E2 are cost and effect of the control (or current practice).
Suppose a person with pancreatic cancer is expected to live for 12 months following diagnosis with a quality of life score of 0.4 (0.4 × 12 months = 0.4 QALYs) and a drug that costs £36,000 can increase life expectancy by 12 months with a quality of life score of 0.8 (0.8 × 24 months = 1.6 QALYs). C1 – C2 = £50,000 and E1 –E2 = 1.6 QALYs – 0.4 QALYs. Therefore ICER = £36,000/1.2 QALYs = £30,000/ QALY.
Incidence
The number of new cases or events during a specified time period.
In 2011, the incidence of lung cancer among males in the UK was 77 new cases per 100,000 males.
Incidence density
See rate.
Latent period
The time interval between acquisition of an infectious agent and the onset of infectiousness.
For measles it can take 7–12 days before a rash appears following an infection and measles is infectious from about 4 days before the rash appears so the latent period for measles is around 3–8 days.
This definition is from ECDC:
- The period between exposure and infection is called ‘latent period’, since the pathogen is present in a ‘latent’ stage, without clinical symptoms or signes of infection in the host.
