Public health and health systems
הוצג| English | משמעות |
|---|---|
| primary prevention | primary prevention |
| secondary prevention | secondary prevention |
| screening | screening |
| tertiary prevention | tertiary prevention |
| over-diagnosis | A real harm. |
Treating a town, not a patient
- A doctor can treat one smoker's lung disease. A ban on smoking indoors can prevent thousands of cases that no doctor will ever see.
- Public health works on whole populations: preventing disease, finding it early, and organising how care is paid for and reached.
Three levels of prevention
- Primary prevention 一级预防 stops disease from starting (vaccination, stopping smoking). Secondary prevention 二级预防 finds it early, before symptoms, mainly by screening 疾病筛查.
- Tertiary prevention 三级预防 limits damage from disease that is already there (rehabilitation after a stroke, palliative care).
- (Fictional) One smoking-related cancer, three levels. Primary: help to stop smoking. Secondary: targeted screening of high-risk people. Tertiary: rehabilitation and palliative care.
- Each level has its own target group and its own measure of success.
Match each activity to its level of prevention.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Primary stops disease starting, secondary finds it early, tertiary limits its damage.
When is screening worth it?
- Screening tests people who feel well. Testing someone who already has symptoms is diagnosis, not screening.
- The classic criteria: the condition is important, it has a detectable early stage, early treatment helps, the test is valid and acceptable, and the programme's benefits outweigh its harms.
Testing a patient who comes in with a breast lump is an example of screening.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
The patient has a symptom, so this is diagnosis. Screening tests people who feel well.
Screening arithmetic
- In a well population most people do not have the disease, so even a good test produces many false positives. The positive predictive value (PPV) falls as the disease gets rarer.
- (Synthetic) 10,000 people, 1% with the disease, sensitivity 90%, specificity 95%. True positives: 90. False positives: 5% of 9,900 = 495. PPV = 90 ÷ 585 ≈ 15%.
(Synthetic) 20,000 people are screened; 0.5% have the disease. Specificity is 98%. How many false positives are expected?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
0.5% of 20,000 = 100 have the disease, so 19,900 do not. 2% of 19,900 = 398 false positives.
(Synthetic) In the same programme sensitivity is 90%, giving 90 true positives beside the 398 false positives. What is the PPV, in % to the nearest whole number?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
PPV = 90 ÷ (90 + 398) = 90 ÷ 488 ≈ 0.18, so about 18%.
The hidden cost: over-diagnosis
- Over-diagnosis 过度诊断 is finding a disease that would never have caused symptoms or death. Those people gain nothing and still bear the tests, worry and treatment.
- A programme is judged by the harms it causes as well as the cases it finds.
Over-diagnosis means —
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
The disease is real but harmless in that person's lifetime, so finding it brings only the costs of testing and treatment.
How health care is paid for
- Beveridge model: funded by general taxation, a national health service (UK). Bismarck model: social insurance paid from wages (Germany).
- Also private insurance and out-of-pocket payment. Each model decides who is covered, who pays at the point of care, and who controls access to specialists.
A system funded mainly by general taxation, with a national health service, is the —
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Beveridge is tax-funded (as in the UK); Bismarck is social insurance from wages (as in Germany).
Common slips
- Calling any early test screening. Screening is for people without symptoms.
- Judging screening by cases found. Count the false positives and over-diagnosis too.
- Comparing systems by spending alone. Coverage and outcomes differ at the same spending.
Recap
- Primary prevents, secondary detects early (screening), tertiary limits damage.
- Screening tests the well; in rare diseases the PPV is low, and over-diagnosis is a real harm.
- Financing models: Beveridge (tax), Bismarck (social insurance), private, out-of-pocket.