为什么在罕见病筛查中，阳性结果常常是假阳性？
Why are positive results so often false when screening for a rare disease?
因为阳性预测值不仅取决于检查性能，还强烈依赖人群患病率。假设某病患病率0.1%，检查敏感性99%、特异性99%，在10万人中约有100名患者，可查出99例真阳性；而99900名健康人中1%被误判，产生999例假阳性。于是阳性者中真正患病的只有约9%。这解释了为什么在低风险人群中盲目做检查会带来大量不必要的复查、焦虑和过度诊断，也是筛查项目要限定目标人群的原因。
Because positive predictive value depends not only on test performance but strongly on the prevalence in the population tested. Suppose a disease affects 0.1% of people and the test is 99% sensitive and 99% specific: among 100,000 people there are about 100 cases, of whom 99 test positive, while 1% of the 99,900 healthy people are misclassified, producing 999 false positives. Only about 9% of positive results are therefore true. This is why testing indiscriminately in low-risk groups generates enormous amounts of unnecessary follow-up, anxiety and overdiagnosis, and why screening programmes define their target population carefully.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
《Gordis流行病学》
Gordis Epidemiology
#阳性预测值 #患病率 #假阳性 #过度诊断
p值小于0.05到底意味着什么？
What does a p-value below 0.05 actually mean?
p值是在“零假设成立”的前提下，观察到当前数据或更极端数据的概率。它不是“假设为真的概率”，也不代表效应有多大、有多重要。美国统计学会2016年的声明明确指出：不应仅以p<0.05作为科学结论或决策的门槛，还必须报告效应量和置信区间，并说明分析计划。反复尝试多种分组和终点直到出现显著结果（所谓p值操纵）会大幅增加假阳性，因此预注册研究方案很重要。
A p-value is the probability of observing the current data, or something more extreme, assuming the null hypothesis is true. It is not the probability that a hypothesis is true, nor does it convey how large or important an effect is. The American Statistical Association's 2016 statement is explicit: p < 0.05 alone should not serve as a threshold for scientific conclusions or decisions, and effect sizes with confidence intervals plus a stated analysis plan must accompany it. Trying many subgroups and endpoints until something turns significant - p-hacking - greatly inflates false positives, which is why pre-registering protocols matters.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#p值 #零假设 #置信区间 #p值操纵
偏倚（bias）与随机误差有何区别？
How does bias differ from random error?
偏倚是系统性的、会朝一个方向歪曲结果的问题（如抽样偏差、测量偏差），无法通过扩大样本消除；随机误差则是偶然波动，靠更大样本和重复可减少。
Bias is a systematic distortion in one direction (e.g., selection or measurement bias) that larger samples cannot fix; random error is chance fluctuation, reduced by bigger samples and replication.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#偏倚 #研究质量
什么是“需治疗人数”（NNT）？
What is the number needed to treat (NNT)?
NNT表示为了多避免一例不良结局，平均需要治疗多少人，等于绝对风险降低的倒数。例如某药把5年心梗风险从4%降到2%，绝对风险降低2%，NNT就是50，意味着治疗50人可多防住1例。相对风险降低50%听起来惊人，但在基线风险很低时绝对获益可能很小，NNT能揭示这种差别。与之对应的NNH表示多造成一例不良反应需治疗的人数，两者并列才能权衡利弊。
The NNT is how many people must be treated, on average, to prevent one additional bad outcome, and it equals the reciprocal of the absolute risk reduction. If a drug cuts five-year heart attack risk from 4% to 2%, the absolute risk reduction is 2% and the NNT is 50 - treat fifty people to prevent one event. A 50% relative risk reduction sounds dramatic, yet when baseline risk is low the absolute benefit may be tiny, and the NNT exposes that difference. Its counterpart, the number needed to harm, shows how many must be treated to cause one adverse event, and the two together allow benefits and harms to be weighed.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-11-04
来源 · Source
Higgins & Green（主编）,《Cochrane Handbook for Systematic Reviews of Interventions》,2008 (DOI: 10.1002/9780470712184)
Higgins & Green (eds.), 'Cochrane Handbook for Systematic Reviews of Interventions', 2008, DOI: 10.1002/9780470712184
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1002/9780470712184
#需治疗人数 #绝对风险降低 #相对风险 #获益权衡
检查的“敏感性”和“特异性”分别指什么？
What do the sensitivity and specificity of a test mean?
敏感性是在确实患病的人中，检查结果为阳性的比例，衡量“抓得全不全”；特异性是在确实没病的人中，结果为阴性的比例，衡量“误伤多不多”。二者通常此消彼长：把判定阈值调低会提高敏感性但降低特异性。因此高敏感性检查适合初筛，阴性结果基本可排除疾病；高特异性检查适合确诊，阳性结果更可信。这也是许多筛查采取“先高敏感、再高特异”两步策略的原因。
Sensitivity is the proportion of people who truly have the disease that the test calls positive - how completely it catches cases; specificity is the proportion of truly healthy people it calls negative - how rarely it mislabels them. The two usually trade off: lowering the cut-off raises sensitivity but lowers specificity. So a highly sensitive test suits initial screening, where a negative result largely rules disease out, while a highly specific test suits confirmation, where a positive result is more trustworthy. That is why many screening programmes use a two-step strategy: sensitive first, specific second.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 来源待核验 · Source pending review
来源 · Source
出处备注：著录仅给书名，无版次与年份；同一书名常对应多个版次，不臆测具体版本。
《Gordis流行病学》
Gordis Epidemiology
#敏感性 #特异性 #诊断试验 #筛查策略
随机对照试验（RCT）为何被视为金标准？
Why is the randomized controlled trial (RCT) considered the gold standard?
RCT 通过随机分配让实验组和对照组在已知未知因素上尽可能可比，再用对照和盲法减少偏倚，因此最能可靠地判断“因”与“果”；但它也有伦理和适用性局限。
RCTs randomly assign participants so groups are comparable, using controls and blinding to minimize bias, making them the most reliable for causality—though limited by ethics and generalizability.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#RCT #循证
“同一健康”（One Health）理念指什么？
What does the One Health concept mean?
One Health 强调人、动物和环境的健康相互关联，主张跨领域合作防控传染病、抗生素耐药和食品安全，因为许多威胁源自三者交界。
One Health recognizes that human, animal, and environmental health are linked, advocating cross-sector cooperation on infectious disease, antibiotic resistance, and food safety, since many threats emerge at their interface.
难度 专业 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#同一健康 #全球健康
疫苗效力（efficacy）与效果（effectiveness）有何不同？
How do vaccine efficacy and effectiveness differ?
效力是理想、受控试验中疫苗防病的百分比；效果是真实世界中的保护率，会受接种覆盖、变异株和人群差异影响，通常略低于效力。
Efficacy is the prevention percentage in ideal controlled trials; effectiveness is real-world protection, affected by coverage, variants, and population differences, usually somewhat lower.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#疫苗效力 #真实世界
什么是人畜共患病（zoonosis）？
What is a zoonosis?
人畜共患病是能从动物传播到人的疾病，如流感、狂犬病和某些冠状病毒；监测动物与人的交界是公共卫生防控的关键。
Zoonoses are diseases transmissible from animals to humans, like flu, rabies, and some coronaviruses; monitoring the animal–human interface is key to public health.
难度 进阶 · 适合 小学低段(6-8)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#人畜共患病 #公共卫生
什么是混杂因素（confounding）？
What is confounding?
混杂是指某个第三变量同时影响暴露和结局、让人误以为二者有关，例如“喝咖啡多的人更爱抽烟”，不控制就会错把吸烟的危害算到咖啡头上。
Confounding is when a third variable affects both exposure and outcome, creating a false link—e.g., heavy coffee drinkers also smoke more, so without control you might blame coffee for smoking's harms.
难度 进阶 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#混杂 #统计
“病死率”和“死亡率”有什么不同？
How do case fatality rate and mortality rate differ?
病死率指某病患者中死亡的比例，反映疾病严重程度；死亡率指某时段总人口中因该病死亡的人数比例，反映人群层面的负担。
Case fatality rate is the share of patients with a disease who die (severity); mortality rate is deaths from it per population over time (population burden).
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#病死率 #死亡率
发病率和患病率有什么区别？
What is the difference between incidence and prevalence?
发病率指一段时间内新发某病的人数比例，反映“风险”；患病率指某个时点患病人数占总人口比例，包含新旧病例，反映疾病负担。
Incidence is the rate of NEW cases over a period (risk); prevalence is the proportion of all cases at a point in time, including old and new, reflecting disease burden.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#发病率 #患病率
“筛查”与“诊断”有什么区别？
What is the difference between screening and diagnosis?
筛查是在无症状人群中找潜在病例（如体检），强调早发现；诊断是针对已有症状者确定具体疾病。筛查阳性还需进一步诊断确认。
Screening looks for potential disease in asymptomatic people (e.g., checkups) to catch it early; diagnosis identifies a specific disease in symptomatic people. A positive screen still needs confirmation.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#筛查 #诊断
“大流行”“流行”和“地方性”的区别是什么？
What is the difference between pandemic, epidemic, and endemic?
地方性是某病在某地长期稳定存在；流行是病例数明显超出平常；大流行是疾病跨多国多洲广泛传播。三者的尺度不同。
Endemic means a disease persists steadily in a region; an epidemic is a clear spike above usual levels; a pandemic is widespread across many countries/continents. They differ in scale.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#大流行 #流行病学
公共卫生和临床看病有什么不同？
How does public health differ from clinical care?
临床医生照顾个体病人，公共卫生则关注整个人群的健康，通过疫苗、清洁水、政策等手段预防疾病、缩小健康差距。
Clinicians care for individual patients; public health focuses on whole populations, preventing disease and reducing health gaps via vaccines, clean water, and policy.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#公共卫生 #预防
什么是 DALY 这种健康负担指标？
What is the DALY health-burden metric?
DALY（伤残调整生命年）把“早死损失的生命年”和“伤残导致的健康年损失”合并，用来比较不同疾病对国家健康的负担，帮助分配卫生资源。
DALY (disability-adjusted life year) combines years lost to early death and to disability, comparing disease burdens to help allocate health resources.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#DALY #卫生经济学
队列研究与病例对照研究有何不同？
How do cohort and case-control studies differ?
队列研究先按是否暴露分组、向前追踪谁发病，适合找原因但耗时；病例对照研究先找病人与对照、回头比暴露史，更快更省但易有回忆偏倚。
Cohort studies group by exposure and follow forward to see who develops disease—good for causality but slow; case-control studies start with cases vs controls and look back at exposures—faster but prone to recall bias.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
《默克家庭医学手册》Merck Manual Home Health Handbook 中译版,人民卫生出版社
The Merck Manual Home Health Handbook, Chinese ed., PMPH
独立核验依据 · Independent verification: 核验依据 2 DOUBAN ISBN 标识 9787117181631（按标识回读: 默克家庭医学手册）
#队列研究 #观察性研究