אפידמיולוגיה והוכחות קליניות
הוצג| English | משמעות |
|---|---|
| incidence/ˈɪnsɪdəns/ | תחלואה (מקרים חדשים) |
| prevalence/ˈprevələns/ | תפוצה |
A decision before an answer
- A thousand existing cases and a hundred new cases answer different questions; mixing them up misreads every health statistic.
- Your goal: Distinguish incidence from prevalence and compute each.
Separate stock from flow
- Incidence counts NEW cases in a period (number of new diagnoses in a year); prevalence counts ALL existing cases at a time.
- Chronic conditions can have low incidence and high prevalence; short acute outbreaks show the reverse. A count of new cases in the United States in the past year is an incidence figure.
A researcher counts the number of new schizophrenia diagnoses in a country during the past year. This statistic is the:
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New cases in a period are incidence; all existing cases would be prevalence.
Give rates denominators
- Rates need denominators: incidence rate is new cases divided by person-time at risk; prevalence is existing cases divided by the population.
- Comparing raw counts across populations of different sizes misleads; compare rates.
Which design follows exposed and unexposed groups forward in time to see who develops the outcome?
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Cohort designs move forward from exposure to outcome; case-control designs look backward.
Climb the evidence ladder
- Case reports, case-control studies, cohorts, randomized trials and meta-analyses answer different questions. Random allocation can reduce baseline confounding under appropriate implementation; observational designs need explicit confounder analysis.
- Quality, bias, relevance and uncertainty must be evaluated within each design. A meta-analysis cannot automatically repair weak constituent studies.
Counting this year's new schizophrenia diagnoses measures incidence; counting everyone currently diagnosed measures prevalence. A 50% relative risk reduction from 2% to 1% is 1 point absolute. A rare-condition screen with many false positives follows directly from the low base rate.
All existing cases of a condition in a population at one time give its ____.
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Prevalence is the stock; incidence is the flow of new cases.
Read risk against baseline
- Screening and risk run on base rates: with low prevalence, even an accurate test yields mostly false positives among positives.
- Number needed to treat and relative versus absolute risk are read against the baseline, not from the treatment label alone.
Reporting a new-case count as prevalence, or quoting relative risk without the absolute baseline.
איזו תשובה מתאימה למקרה זה?
להבחין בין תדירות (incidence) לנפוצות (prevalence) ולחשב כל אחת מהן
A condition can have low incidence and high prevalence at the same time.
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Chronic conditions accumulate: few new cases each year but many existing ones.
Keep the distinctions
- incidence 发病率(新发病例) — The number or rate of NEW cases arising in a period.
- prevalence 患病率 — The proportion of a population with the condition at a given time.
- Distinguish incidence from prevalence and compute each.
- Evaluate clinical evidence by design strength.
- Interpret risk, screening and base rates in populations.
Match each term with its precise meaning in this lesson.
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Keep the distinctions stated in the teaching example.
Put this lesson’s reasoning or event sequence in order.
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The order follows the stated process; check each stage before the next.