描述性研究

1. 描述性研究 Descriptive Study 哈尔滨医科大学流行病学教研室 Department of epidemiology ，Harbin Medical University

2. Methods of study three types of basic methods Observational Cross-sectional study Ecological study Descriptive study Case-control study Cohort study Analytic study Clinical trial Field trial Community intervention Experimental Theoretical

3. Epidemiology is the study of thedistributionanddeterminants of diseasefrequency in human population. Epidemiology: Principles and Methods byBrian MacMahon 1996

4. ? The distribution of Disease considers • Who is getting disease? • Where is disease occurring? • When is disease occurring?

5. Descriptive Epidemiology Cases Time Person Place Who? Where? When?

6. Descriptive studyis to subset collected data or some survey data, included the data from experiment, to groups by different places, different time or different population character and descriptive the frequency of disease and health. Helps to build the relationship between risk factors and disease or health, offer etiological clues. 描述性研究通过描述疾病或健康状况的三间分布情况，找出某些因素与疾病或健康状况间的关系，提供病因线索。

7. 现况研究的概述 现况研究的设计与实施 研究实例 生态学研究 Introduction of cross-sectional study Design and implementation of cross-sectional study A case study Ecological study Outline 目 录

8. 第一节 现况研究概述Introduction of Cross-sectional Study • 基本概念　 • 目的与应用 • 特点与类型 • Basic concept • Mechanism Purposes and applications • Characteristics and categories

9. 一、基本概念 Conception • 又称横断面研究也称患病率研究 • 时点或期间和特定范围内人群中的有关变量(因素)与疾病或健康状况的关系 • Cross-sectional study or prevalence study • Describes the relationship between disease or health and variables (factors) in the population at a particular point of time or period

10. DZ DZ E E - Time

11. T2 T1 T3 Time Schematic diagram of Cross-sectional Study

12. 二、目的与应用 Mechanism Purposes and applications • 掌握目标群体中疾病或健康状况的分布 • 提供疾病病因研究的线索 • Describes the distributing of disease or health events within populations • To provide etiological clues

13. This figure shows the infant death frequency (per 1000 live births) in different countries

14. 二、目的与应用 Mechanism Purposes and applications • 确定高危人群 • 评价疾病监测、预防接种等防治措施效果 • To identify high risk groups in the population • To evaluate the effect of surveillance，vaccination and disease prevention and control

15. 三、特点与类型 Characteristics and categories • 研究特点 • 开始时一般不设对照组 • 现况研究的特定时间 • 在确定因果联系时受到限制 • 对不会发生改变的暴露因素，可以提示因果联系 • Characteristics • No control group • Particular point of time • Limit to ensure the causal relationship • To prompt causal relationship for the exposures that won’t be changed

16. 三、特点与类型 Characteristics and categories • 研究类型 • 普查 • 抽样调查 • Category • Census • Sampling survey

17. The census of the lifetime alcohol drinking status in America population

18. 第二节 现况研究的设计与实施 Design and implementation of cross-sectional study • 明确调查目的和类型 • 确定研究对象 • 确定样本量和抽样方法 • 资料的收集 • 资料的整理与分析 • 常见偏倚及其控制 • 研究的优点与局限性 • To make the purpose and category of study • To select the objects • To determine the sample size and sampling method • To collect data • To sort and analyze data • Bias and control • Advantage and limitation

19. 一、明确调查目的和类型To make the purpose and category of study • 根据研究提出的问题，明确调查目的 • 根据具体研究目的确定是普查还是抽样调查 • To make the purpose by the proposal of the study • To select the survey method reference to the aim, census or sampling survey.

20. 二、确定研究对象To select the objects • 某个区域内的全体居民或其中一部分 • 某一时点上的流动人员 • 某些特殊群体 • Entire or part of the population in a region • Floating population at a particular point of time. • Certain special groups of people

21. 三、确定样本量和抽样方法To determine the sample size and sampling method • 确定样本量 • 预期现患率 ( P ) • 允许误差（d） • 显著性水平（α） • To determine the sample size • Expected prevalence( P ) • Allowable error（d） • Significance level（α）

22. 计量资料样本大小估计公式 Formulas for Numerical data 计数资料样本大小估计公式 Formulas for Categorical data

23. 抽样方法 Sampling Method • 非随机抽样 Non-random sampling • 随机抽样 Random sampling

24. 非随机抽样 Non-random sampling 选择样本时，加入人主观因素，使总体中每个个体被抽取的机会是不均等的 Non-random samples are selected by any kind of procedure that does not give all cases in the population equal chances to fall into the sample.

25. 随机抽样 Random sampling 总体中每一个对象都有同等机会被选入作为研究对象 Every person in the target population has the same known (and non-zero) chance of being included in the survey

26. 随机抽样 Random sampling 方 法 Methods Simple random sampling Systematic sampling Clustering sampling Stratified sampling Multistage sampling 单纯随机抽样 系统抽样 整群抽样 分层抽样 多级抽样

27. 单纯随机抽样(简单随机抽样) Simple random sampling • 最简单、最基本的抽样方法 • 从总体N个对象中，利用抽签或其他随机方法抽取n个 • 总体中每个对象被抽到的概率相等 • Simplest and basic method • To select numbern subjects by drawinglot or by using a table of random number from population with N units • Equal chance for each subject in the target population

28. 图3－1 总体与样本示意图 Fig 3－1 Diagram of population and sample

29. 系统抽样(机械抽样) Systemic sampling • 将总体各个个体单位按某种标志排列、连续编号 • 根据总体数N和确定的样本数n，计算抽样距离（N/n） • Rank every units by a character construct and number them • Define the size of the sample and calculate sampling interval (k = N/n)

30. 系统抽样(机械抽样) Systemic sampling 3. 用单纯随机方法在第一组中确定一个起始号 4. 从此起始点开始，每隔K（K=N/n）个单位抽取一个作为研究对象 3. Draw a random number ( k) for starting 4. Draw every k units from first unit

31. 图3－2 系统抽样示意图 Fig 3－2 Diagram of systemic sampling

32. Example: Systematic sampling

33. 整群抽样 Cluster sampling 将总体分成若干群组，抽取其中部分群组作为观察单位组成样本 The entire population of interest is divided into groups, or clusters, and a random sample of these clusters is selected. 单纯整群抽样（Simple cluster sampling） 二阶段抽样（Two stages sampling）

34. 图3－3 整群抽样示意图 Fig 3－3 Diagram of cluster sampling

35. Example: Cluster sampling Section 1 Section 2 Section 3 Section 5 Section 4

36. 分层抽样 Stratified sampling 将总体单位按某种特征分为若干次级（层），然后从每一层内单纯随机抽样组成一个样本。 First, stratify the population into several strata by character of areas, ages, etc. then select objects using random sampling in each strata.

37. 分层抽样 Stratified sampling 按比例分配（proportional allocation） 最优分配（optimum allocation)

38. 图3－4 分层抽样示意图 Fig 3－3 Diagram of cluster sampling

39. Example: stratified sampling

40. 多级抽样 Multistage sampling 将抽样过程分阶段进行，每个阶段使用的抽样方法往 往不同，即将以上抽样方法结合使用，在大型流行病 学调查中常用。 Multi-stage samplingis a kind of complex sample design in which two or more levels of units are imbedded one in the other.

41. 多级抽样 Multistage sampling …… 二级抽样单位 Secondary units 一级抽样单位 Primary units ……

42. 五、资料的整理与分析 Data sort and analysis • 检查资料完整性和准确性 • 按标准归类、核实 • Check the integrity and accuracy of data • Classify and verify data by standard

43. Target Population or Sampling Frame Census or Sampling Survey Sample Disease And Exposure Disease and Non-exposure Non-disease and Exposure Non-disease and Non-exposure

45. 80 Healthy 80 well Job A (hazardous) 100 Workers 20 Respiratory symptoms 10 well 95 Healthy 95 well Job B (hazardous) 100 Workers 5 Respiratory symptoms 15 well Point Y Point X Prevalence rate of respiratory symptoms in Job A 20%(20/100) 11%(10/90) 14%(15/110) Prevalence rate of respiratory symptoms in Job B 5%(5/100) Ratio of prevalence rates, Job A/Job B: 4.0 0.8 Example:

46. Prevalence of hypertension by age and sex Cork and Kerry Diabetes & Heart Disease Study, 1998

47. Example of Cross-Sectional Study Hypothesis: Obesity is a risk factor for knee osteoarthritis Sample: 100 retirees living at “University Village”

48. Medical exam + X-rays to diagnose osteoarthritis of the knee Osteoarthritis - + + 40 10 50 Obesity - 20 30 50

49. Prevalence of osteoarthritis among obese subjects: 40/50 = 0.8 Prevalence of osteoarthritis among non-obese subjects: 20/50 = 0.4 Prevalence ratio = 0.8/0.4 = 2.0

50. Obese subjects are two times more likely to have osteoarthritis of the knee than non-obese subjects.