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Guangzhou Epidemiology Training Course 2010 May 29-31 Jing Xie, 谢晶 Instructor: 谢晶, Jing Xie jxie@hsph.harvard.edu Department of Epidemiology, School of Public Health, Harvard University May 29 AM Course Overview & Epidemiology Concept ?Course Overview ?Course Objectives ?To provide introductory knowledge in epidemiology and its application in etiology research. ?To provide an orientation to epidemiology as a basic science for public health and clinical medicine. ?To address the principles of the quantitative approach to clinical and public health problems. ?To provide participants better understanding of epidemiology research and medical research papers. ?To give you a set of tools and a way of thinking as an epidemiologist ?Bottom line: If you never consider the results of a study the same again, this course will have been a success ?Readings and textbooks ?See syllabus ?Epidemiology ≠流行病学 ?Epidemiology in Medicine is just like Economics in business, which is a tool can be applied to solve medical questions. ?Widely used in medical research : Nutritional、Genetics、Molecular Biology、Health policy and management、Pharmaceutical ?Epidemiology ?Epidemiology is the study of the distribution, determinants, and frequency of diseases in human population. Root word: Epidemic (infectious disease) ?Epidemiology, "the study of what is upon the people", is derived from the Greek terms: epi = upon, among; demos = people, district; logos = study, word, discourse; suggesting that it applies only to human populations. ?流行病学(epidemiology)是研究特定人群中疾病、健康状况的分布及其决定因素,并研究防治疾病及促进健康的策略和措施的科学。 ?Questions can be solved by epidemiology ?Can brain cancer be caused by use of cell phones? ?Should women of childbearing age be concerned about mercury in fish? ?Will taking vitamin D supplements reduce risk of chronic diseases? ?What is the minimum amount of exercise we have to do to lower our risk of heart disease? diabetes? cancer? ?What is the long term impact of pesticides in food? ?因此,流行病学又称方法学,是广大基层卫生人员和乡村医生从事防治工作时必备的预防医学知识。 ?同时在临床工作和药效方面也常采用流行病学的分析方法,探讨和解决存在的问。 ?Hypothetical scenarios ?According to a review of 4,000 patients who had cancer, 2/3 of these patients had at some time weighed 15% or more above the norm for their sex and age. ?Conclusion: Obesity is associated with cancer. ?What do you think? . . . ?The mortality rate (死亡率) per 1,000 population in Guangdong is 4.8 compared to 14.5 in Sichuan. Conclusion: Guangdong is a more healthy environment. ?What do you think? . . . ?Handedness and Life Span N Engl J Med, April 4, 1991, p 998 ?Observation that proportion of left-handers in the population decreases substantially with age led to suggestion that sinistrality may be associated with decreased life span. ?Sent questionnaires to next of kin of 2000 individuals who died in southern California. 967 responded, with information about whether person was right-handed or non-right-handed (left or mixed). ?Mean age of death: ? right-handed: 75 years ? left-handed: 66 years p <0.0001 ?significantly more left-handers died in accidents, or in accidents while driving a vehicle ?Conclusion: "These results are consistent with predictions based on implied pathological factors and environmental interactions, suggesting that left-handers are at greater risk of death at any given age." ?What do you think? . . . ? A study of 250 patients who had angina pectoris was initiated. Five years later, 200 of these patients were contacted to obtain follow-up data. Of these 200 patients, 26% had died, in 20% symptoms had worsened, and in 54% symptoms remained the same. Conclusion: The five-year survival rate for angina pectoris was 74%. ?What do you think? . . . ?流行病学研究方法类型 ?Descriptive studies (描述性研究) ?Analytical studies (分析性研究) “流行病学基本上是一门归纳性的科学”(Frost,1941)。流行病学从“描述”与“分析”两方面来体现它的归纳性。在描述中注重分析,在分析中贯穿描述。 ?Descriptive studies (描述性研究) ?Descriptive studies are concerned with describing the general distribution of disease in space and time (cross-sectional studies). ?所谓描述性研究即人们常说的描述流行病学,是将所得资料按不同地区、不同时间以及不同人群特征分组,将疾病、健康或卫生事件的分布情况真实地展示出来。人们往往会从其结论中获得启迪,引导人们进一步的探索与研究。 ?Distribution ?How common? ?Who is affected? ?When does it occur? ?Where does it occur? ?How common or unusual is disease occurrence ?Rare (sporadic) disease ?Endemic disease ?Epidemic disease ?Pandemic disease ?Rare (sporadic) disease has no accepted definition ?The Rare Disease Act of 2002 defines a rare disease as one that affects less than 200,000 persons in the US ?Wilkipedia defines a rare disease as one which occurs so infrequently that a doctor in a busy general practice would not expect to see more than one case a year ?NOTE: disease can be rare in some areas and common elsewhere. It can be rare now but common in the past (or future). ?Endemic: usual presence of a disease within a given population ?Epidemic: occurrence of a disease clearly in excess of normal expectancy in a defined community or region ?Pandemic: worldwide epidemic ?描述分布的常用测量指标(Measurement of disease frequency):发病率(Incidence)、现患率(Prevalence)、死亡率(Mortality)、病死率(morbidity)的意义、用途与计算方法。 描述疾病流行强度的常用语:爆发、散发、流行和大流行;疾病的三间分布(时间、空间、人群)的概念及主要内容。病因的定义及病因推断的。 ?Analytical studies (分析性研究) ?Analytic studies are concerned with causes and prevention of disease (case-control studies, cohort studies). ?所谓分析性研究,从方法学上来看是指那些已发展成熟的方法如观察性研究(observational studies)、实验性研究(experimental studies)以及数学模型研究(statistical modeling)。 ?The most common health-related states and events in epidemiologic research are death and disease ?How do you know someone has a disease? ?In individuals –Ask the person –Ask the doctor –Review medical records ?In populations –Use active surveillance –Rely on reporting ?How do you know someone is dead and what was the cause of death? ?In individuals –Call and ask –Ask next-of-kin –Review medical records ?In populations –Examples include understanding of the meaning of an odds ratio (OR), a confidence interval (CI), and different epidemiologic study designs: randomized clinical trial, case-control study, and cohort study. ?人们对某一医疗、卫生事件深入的认识都需要反复经历描述性研究与分析性研究的过程。在描述性研究的基础上可以比较容易地开展分析性研究,而当一项或多项分析性研究结束后,往往需要对此在更高的层次上做描述性研究,如此循环不已,直至事物的本质得到充分的揭示,完成从具体描述到宏观描述,从初步分析到深入分析的飞跃。 ?Timing ?Prospective ?Retrospective Measurement of Disease Frequency Four simple mathematical parameters: Count Simple measure of quantity Example: Number of cancer patients at Sun Yat-sen University Cancer Center in 2009 Ratio Obtained by dividing one quantity by another. These quantities may be related or may be independent. Example: Number of stillbirths per thousand live births. Proportion A ratio in which the numerator is included in the denominator Example: The number of fetal deaths out of the total number of births (expressed as %) Rate A measure of how quickly something of interest happens Example: The number of births in a year in Guangzhou Measures of Disease Frequency Incidence (I): Measures new cases of a disease that develop over a period of time. Prevalence (P): Measures existing cases of a disease at a particular point in time or over a period of time. ?Incidence Reflects transition from disease-free to affected state ?Mortality Reflects transition from alive to dead ?Incidence Reflects transition from disease-free to affected state ?Cumulative Incidence (CI) ?Problems with using CI ?To accurately calculate CI we need to follow the entire population for the specified time interval. ?This is rarely possible for two main reasons –People move in and out (dynamic cohort) –People may die from diseases other than disease of interest (competing risks) ?Incidence rate (IR) ?Rates ?What is the Risk of Disease X? ?What is the Risk of Disease X? ?Confusing Risk with Rate Which ones of these “rates” are true rates? ?Attack rate ?Incidence rate ?Five-year survival rate ?Infant mortality rate ?Mortality rate ?Prevalence rate ?Age-specific incidence rate ?Case-fatality rate ?Cause-specific mortality rate ?Confusing Risk with Rate ?Prevalence vs. Incidence ?Prevalence can be viewed as describing a pool of disease in a population. ?Incidence describes the input flow of new cases into the pool. ?Fatality and recovery reflects the output flow from the pool. ?Prevalence ?Measures existing cases of a health condition ?Primary feature of a cross-sectional study ?Two types of Prevalence ?Point prevalence ?Period prevalence ?Point Prevalence C = # of observed cases at time t N = Population size at time t Measures the frequency of disease at a given point in time ?Point Prevalence Example Suppose there are 150 individuals in a population and, on a certain day, 15 are ill with the flu. What is the estimated prevalence for this population? ?Period Prevalence ? C = the # of prevalent cases at the beginning of the time period.