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流行病学·公共卫生
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流行病学·公共卫生
12
engines
基本再生数 R0
Basic reproduction number R0
R0=β/γ · 有效Rt=R0·S/N · 阈值R0=1 · 代际树
How many secondary cases one infection causes — and how Rt falls as immunity grows
Herd immunity threshold
Herd immunity threshold
Hc=1−1/R0 · 所需免疫比例 · S<1/R0不增长
Hc = 1 − 1/R₀ · the outbreak cannot grow once the immune fraction crosses it
Contact tracing & branching spread
Contact tracing & branching spread
分支传播 · 追踪比例压Rt<1 · 疫情熄灭
Effective R = R₀(1 − t) · tracing pulls R below 1 and the outbreak collapses
Incidence, prevalence & duration
Incidence, prevalence & duration
患病率≈发病率×病程 · 点/期患病率 · 累积发病
Steady state: prevalence ≈ incidence rate × average duration
Case fatality vs infection fatality
Case fatality vs infection fatality
CFR=死亡/病例 · vs IFR÷感染 vs 死亡率÷人口
Same deaths, different denominators: CFR, IFR and crude mortality
Attack rate & outbreak attribution
Attack rate & outbreak attribution
罹患率=病例/暴露 · 续发率 · 食源2×2找元凶
AR = cases / people-at-risk · find the culprit food by the AR ratio
Sensitivity & specificity
Sensitivity & specificity
2×2 TP/FP/FN/TN · Se/Sp · ROC点
A diagnostic test as a 2×2 table · Se and Sp are column ratios
Screening & predictive value
Screening & predictive value
PPV/NPV贝叶斯 · 低患病率PPV崩塌 · 人群网格
PPV / NPV by Bayes · why a good test fails at low prevalence
Vaccine efficacy
Vaccine efficacy
VE=1−RR · 两组罹患率 · RR=接种/未接种
VE = 1 − RR · comparing attack rates between two trial arms
Odds ratio & relative risk
Odds ratio & relative risk
OR=ad/bc · RR相对危险度 · 罕见病OR≈RR
A 2×2 exposure–outcome table · RR for cohorts, OR for case-control
Cohort life table
Cohort life table
qx/lx/dx/Lx/Tx/ex · 生存曲线 · 期望寿命
From age-interval mortality qx to survivors lx and life expectancy ex
Epidemic curve
Epidemic curve
按发病日直方图 · 点源vs人传人 · 暴露窗口
Case counts by onset · point-source vs propagated · exposure window