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© 2004 Aeras Global TB Vaccine Foundation Clinical Research Practice Epidemiology & Biostatistics 2.

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Presentation on theme: "© 2004 Aeras Global TB Vaccine Foundation Clinical Research Practice Epidemiology & Biostatistics 2."— Presentation transcript:

1 © 2004 Aeras Global TB Vaccine Foundation Clinical Research Practice Epidemiology & Biostatistics 2

2 © 2004 Aeras Global TB Vaccine Foundation 2 Epidemiology & Biostatistics 2 This course will help you to understand: Epidemiological and biostatistical terms and concepts. Epidemiological and biostatistical terms and concepts. How epidemiology and biostatistical methods play a role in your work. How epidemiology and biostatistical methods play a role in your work. Typical research articles and protocols. Typical research articles and protocols.

3 © 2004 Aeras Global TB Vaccine Foundation 3 You will learn to: Differentiate between a descriptive and an analytic epidemiological study. Differentiate between a descriptive and an analytic epidemiological study. Given a study objective, identify the type of study and study design. Given a study objective, identify the type of study and study design. Identify what determines the study design and data to be collected. Identify what determines the study design and data to be collected. Identify 5 common outcome measures and define each of them. Identify 5 common outcome measures and define each of them.

4 © 2004 Aeras Global TB Vaccine Foundation 4 You will learn to: Define bias in the context of a research study and identify 2 types of bias. Define bias in the context of a research study and identify 2 types of bias. Explain why randomization and blinding are important. Explain why randomization and blinding are important. Differentiate between active and passive follow-up and identify the advantages and disadvantages of each. Differentiate between active and passive follow-up and identify the advantages and disadvantages of each.

5 © 2004 Aeras Global TB Vaccine Foundation 5 You will learn to: Define sampling and explain why this procedure is useful in clinical research. Define sampling and explain why this procedure is useful in clinical research. State three ways that data can be collected to test a hypothesis. State three ways that data can be collected to test a hypothesis. Differentiate between categorical and continuous data and state the characteristics of each. Differentiate between categorical and continuous data and state the characteristics of each.

6 © 2004 Aeras Global TB Vaccine Foundation 6 You will learn to: Define Biostatistics. Define Biostatistics. Define counts, proportions and rates and identify what each measures. Define counts, proportions and rates and identify what each measures. Differentiate between rates, counts and proportions. Differentiate between rates, counts and proportions. Identify the three ways to summarize continuous data and define each method. Identify the three ways to summarize continuous data and define each method.

7 © 2004 Aeras Global TB Vaccine Foundation 7 Remember Epidemiology? Epidemiology is a branch of medical science that studies a group of people to see: who has disease (young/old, male/female) who has disease (young/old, male/female) where is the disease occurring (urban/rural, Africa/Europe, etc.) where is the disease occurring (urban/rural, Africa/Europe, etc.) why people get disease (environmental, genetic, etc) why people get disease (environmental, genetic, etc) what is associated with disease and health (diet, other disease, environment, etc) what is associated with disease and health (diet, other disease, environment, etc) With the goal of preventing disease and promoting good health.

8 © 2004 Aeras Global TB Vaccine Foundation 8 Ongoing survey to see who gets sick - surveillance of disease and general health. Ongoing survey to see who gets sick - surveillance of disease and general health. Study outbreaks of disease - investigation of disease. Study outbreaks of disease - investigation of disease. How and why people get sick - analytic studies. How and why people get sick - analytic studies. Study effectiveness of public health programs - evaluation of health programs. Study effectiveness of public health programs - evaluation of health programs. How Does Epidemiology Promote Good Health?

9 © 2004 Aeras Global TB Vaccine Foundation 9 In epidemiology, studies fall into two main types with different purposes. Descriptive Descriptive Analytical Analytical Types of Studies

10 © 2004 Aeras Global TB Vaccine Foundation 10 Descriptive Epidemiology The study of the amount of disease and where disease occurs, looking for trends based on person, place, and time. Descriptive studies organize and summarize health data by groups that describe: Who has the disease. Who has the disease. Where the disease occurs. Where the disease occurs. When the disease happens. When the disease happens.

11 © 2004 Aeras Global TB Vaccine Foundation 11 Examples of Descriptive Studies Study the seasonality of malaria outbreaks in Northern KwaZulu(Nov-May/June). Helps health departments plan distribution of bed nets and mosquito spraying campaigns. Study the seasonality of malaria outbreaks in Northern KwaZulu(Nov-May/June). Helps health departments plan distribution of bed nets and mosquito spraying campaigns. Study cases of malaria, by analyzing data by where the disease was acquired helps to identify areas at high risk of malaria. Study cases of malaria, by analyzing data by where the disease was acquired helps to identify areas at high risk of malaria.

12 © 2004 Aeras Global TB Vaccine Foundation 12 Descriptive Study: Age Specific Rates of TB in the Cape Metropole Data from Provincial Authority Western Cape Province, Unpublished Data 2004, courtesy of Dr. Hassan Mohamed

13 © 2004 Aeras Global TB Vaccine Foundation 13 Analytic Epidemiology The search for health-related causes and effects. Uses comparison groups to quantify the link between exposures and outcomes and test hypotheses about causal relationships. Analytic studies can answer questions not answered by descriptive studies by searching for the cause of the disease by: finding out the relationship between disease and other factors. finding out the relationship between disease and other factors. testing theories about the cause of disease. testing theories about the cause of disease.

14 © 2004 Aeras Global TB Vaccine Foundation 14 Examples of Analytic Studies Hepatitis A outbreak: Almost all infected drink city water and ate pastries from the same pastry shop. Almost all infected drink city water and ate pastries from the same pastry shop. A control group of healthy people is questioned. Find almost all healthy people drink city water, but few ate the same pastries. A control group of healthy people is questioned. Find almost all healthy people drink city water, but few ate the same pastries. Results indicate pastries from this particular shop are a risk factor for hepatitis A. Results indicate pastries from this particular shop are a risk factor for hepatitis A.

15 © 2004 Aeras Global TB Vaccine Foundation 15 Activity: Can you tell the difference between a descriptive and an analytic study?

16 © 2004 Aeras Global TB Vaccine Foundation 16 How is a study done?

17 © 2004 Aeras Global TB Vaccine Foundation 17 State the research question & formulate hypothesis. State in detail the question to be answered. State the research question & formulate hypothesis. State in detail the question to be answered. Choose the appropriate Study Design. Decide the best way to answer research question. Choose the appropriate Study Design. Decide the best way to answer research question. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Analyze the data. Analyze the data. Use biostatistics to examine data. Report your findings. Share what you learn so findings can be used to improve public health. Report your findings. Share what you learn so findings can be used to improve public health. Epidemiology Research Process

18 © 2004 Aeras Global TB Vaccine Foundation 18 State the Research Question When a public health problem is identified, the situation is explored before focusing on a specific research project. Why is the situation important? Why is the situation important? Why do you want to study the situation? Why do you want to study the situation? What do you really want to know? What do you really want to know? What will tell you that the disease or situation exists? What will tell you that the disease or situation exists?

19 © 2004 Aeras Global TB Vaccine Foundation 19 Formulate a Hypothesis After the research question is clarified, typically the next step is to write a hypothesis. A hypothesis is a testable or refutable prediction of what you expect as your study results, based on the question of interest. A hypothesis is a testable or refutable prediction of what you expect as your study results, based on the question of interest.

20 © 2004 Aeras Global TB Vaccine Foundation 20 Define The Outcome Of Interest In the hypothesis, the outcome of interest also needs to be identified and defined. In the hypothesis, the outcome of interest also needs to be identified and defined. Outcomes are the endpoints or signals that the disease or situation being studied exists. Outcomes are the endpoints or signals that the disease or situation being studied exists.

21 © 2004 Aeras Global TB Vaccine Foundation 21 Common Outcome Measures For Clinical Research Studies Mortality Mortality Morbidity Morbidity Prevalence Prevalence Incidence Rate Incidence Rate Change in physiological measurement or parameter Change in physiological measurement or parameter

22 © 2004 Aeras Global TB Vaccine Foundation 22 Common Outcome Measures For Clinical Research Studies Mortality A measure of the incidence of deaths in a population expressed as a rate or a proportion. Mortality A measure of the incidence of deaths in a population expressed as a rate or a proportion. Morbidity Any departure, subjective or objective, from a state of physiological or psychological well- being. Also the frequency of a disease or of all diseases in a population. Morbidity Any departure, subjective or objective, from a state of physiological or psychological well- being. Also the frequency of a disease or of all diseases in a population.

23 © 2004 Aeras Global TB Vaccine Foundation 23 Common Outcome Measures For Clinical Research Studies Prevalence Prevalence The proportion of persons in a population who have a particular disease at a specified point in time. The proportion of persons in a population who have a particular disease at a specified point in time. Expressed as number of cases per 100,000 people. Expressed as number of cases per 100,000 people. Incidence Rate Incidence Rate A measure of the frequency with which a new case of illness occurs in a population over a period of time. A measure of the frequency with which a new case of illness occurs in a population over a period of time. Rate is usually expressed as number of cases per 100,000 per year. Rate is usually expressed as number of cases per 100,000 per year.

24 © 2004 Aeras Global TB Vaccine Foundation 24 Common Outcome Measures For Clinical Research Studies Change in physiological measurement or parameter Change in physiological measurement or parameter Any change in health status that can be measured. Any change in health status that can be measured. Examples: Examples: Height Height Weight Weight Lab test results Lab test results Mantoux skin test results Mantoux skin test results BMI (body mass index) BMI (body mass index) Change in x-rays of a patients lung showing TB Change in x-rays of a patients lung showing TB

25 © 2004 Aeras Global TB Vaccine Foundation 25 State the research question & formulate hypothesis. State in detail the question to be answered. State the research question & formulate hypothesis. State in detail the question to be answered. Choose the appropriate Study Design. Decide the best way to answer research question. Choose the appropriate Study Design. Decide the best way to answer research question. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Analyze the data. Analyze the data. Use biostatistics to examine data. Report your findings. Share what you learn so findings can be used to improve public health. Report your findings. Share what you learn so findings can be used to improve public health. Epidemiology Research Process

26 © 2004 Aeras Global TB Vaccine Foundation 26 Choose Study Design What determines study design? What determines study design? What factors might affect the effectiveness or validity of the study design and ultimately the study results? What factors might affect the effectiveness or validity of the study design and ultimately the study results?

27 © 2004 Aeras Global TB Vaccine Foundation 27 Review Study Designs Retrospective Study: Collect data from the past. Retrospective Study: Collect data from the past. Cross-sectional Study: Collect data at the present point in time. Cross-sectional Study: Collect data at the present point in time. Prospective Study: Collect data from start of the study & follow into the future. Prospective Study: Collect data from start of the study & follow into the future.

28 © 2004 Aeras Global TB Vaccine Foundation 28 What Determines Study Design? The research question! The research question helps guide the study design. The study design shows: The research question helps guide the study design. The study design shows: how the question will be answered. how the question will be answered. what data need to be collected. what data need to be collected. Choose a study design that will most reliably answer the question. Choose a study design that will most reliably answer the question.

29 © 2004 Aeras Global TB Vaccine Foundation 29 What Else Can Affect Study Design? Protection of Human Participants Protection of Human Participants The study must be ethically sound and not overly invasive for study participants. If the approach to the science is bad, the study is unethical. Costs and Logistics Costs and Logistics Feasibility of doing the study is important. The practicalities of doing the study must be considered. And the costs of implementing a study design should not exceed the resources available.

30 © 2004 Aeras Global TB Vaccine Foundation 30 What Else Can Affect Study Design? Validity of Results Validity of Results Good study design ensures that the study results are accurate, well-founded with defensible answers. Underlying Nature of the Disease Underlying Nature of the Disease Factors of the disease impact design, like a long life cycle of disease, rarity of certain events, etc. Population Being Studied Population Being Studied If the population is stable or likely to migrate.

31 © 2004 Aeras Global TB Vaccine Foundation 31 Other Elements of Study Design: Follow-Up Follow-up is the act of observing an individual or population to: Check the relevant characteristics that have previously been assessed and documented. Check the relevant characteristics that have previously been assessed and documented. Observe any changes in those same characteristics or overall health status over a specified period of time. Observe any changes in those same characteristics or overall health status over a specified period of time.

32 © 2004 Aeras Global TB Vaccine Foundation 32 Active vs. Passive Follow-Up Active Follow-Up When contact is made with all individuals in the group to check for changes in status at specific points in time. Passive Follow-Up When no contact is made with individuals. Changes in status are identified by searching health records.

33 © 2004 Aeras Global TB Vaccine Foundation 33 Active Follow-Up Advantages: Relatively accurate reporting Relatively accurate reportingDisadvantages: Expensive More difficult to do May not be possible to determine if other factors not studied are the cause of change in characteristics.

34 © 2004 Aeras Global TB Vaccine Foundation 34 Passive Follow-Up Advantages: Relatively cheap Relatively cheap Relatively easy to do Relatively easy to doDisadvantages: Under-reporting likely Easy to miss local outbreaks Can rarely do more than indicate areas for further study

35 © 2004 Aeras Global TB Vaccine Foundation 35 Another Study Design Issue Bias is… Any process or effect that produces results that differ from the truth in a systematic way. or A systematic action that has the effect of “playing favorites” in choosing study subjects or assessing exposure.

36 © 2004 Aeras Global TB Vaccine Foundation 36 Two Types of Bias Selection Bias: Wrong people in the study sample. Misclassification Bias: Right people, wrong or inaccurate information.

37 © 2004 Aeras Global TB Vaccine Foundation 37 Occurs when participants in a study do not represent the population from which they are selected. This happens when: not everyone eligible to be in a study can be selected as a subject. not everyone eligible to be in a study can be selected as a subject. those selected are different from those excluded, in a systematic way. those selected are different from those excluded, in a systematic way. Selection Bias

38 © 2004 Aeras Global TB Vaccine Foundation 38 Misclassification Bias Bias arising from errors in classification of the exposure or disease status of the study participants.

39 © 2004 Aeras Global TB Vaccine Foundation 39 Important Strategies to Minimize Bias and Ensure Valid Results Randomization – study participants are grouped to receive different interventions arbitrarily. Randomization – study participants are grouped to receive different interventions arbitrarily. Blinding – participants and research staff are not aware of details of treatment or who receives what intervention. Blinding – participants and research staff are not aware of details of treatment or who receives what intervention. Blinding procedures vary, so different groups of staff and sponsor may be blinded, depending on the study.

40 © 2004 Aeras Global TB Vaccine Foundation 40 Aspects of Study Design: Sampling When research is conducted, it is often impractical to include the entire population, so a sample of the target population is studied. Sample is a subset of the target population.

41 © 2004 Aeras Global TB Vaccine Foundation 41 Types of Sampling Methods Probability Sampling: Non-Probability Sampling: Generates a sample that is likely to be representative of the population. Generates a sample that is likely to be representative of the population. Each member of the population has an equal chance of inclusion in the sample. Each member of the population has an equal chance of inclusion in the sample. Cannot be sure if the sample represents the population. Cannot be sure if the sample represents the population. Members of sample chosen based on convenience, location or other possibly biased selection method. Members of sample chosen based on convenience, location or other possibly biased selection method.

42 © 2004 Aeras Global TB Vaccine Foundation 42 How Is a Probability-based Sample Selected? Sampling methods uses some form of random selection to ensure that each subject has an equal chance of being selected. 1. Create a list of all possible subjects. This is the sampling frame. 2. Decide the proportion of subjects you want to select. This is the sampling fraction. 3. Choose a systematic way to select your sample at random from the list of possible subjects. 4. The result is your sample.

43 © 2004 Aeras Global TB Vaccine Foundation 43 Why Is Probability Sampling Better? It allows one to draw some conclusions about the target population without including everyone in the study. It allows one to draw some conclusions about the target population without including everyone in the study. Sampling strategies are used to make sure that the sample is an accurate representation of the population. Sampling strategies are used to make sure that the sample is an accurate representation of the population.

44 © 2004 Aeras Global TB Vaccine Foundation 44 State the research question & formulate hypothesis. State in detail the question to be answered. State the research question & formulate hypothesis. State in detail the question to be answered. Choose the appropriate Study Design. Decide the best way to answer research question. Choose the appropriate Study Design. Decide the best way to answer research question. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Analyze the data. Analyze the data. Use biostatistics to examine data. Report your findings. Share what you learn so findings can be used to improve public health. Report your findings. Share what you learn so findings can be used to improve public health. Epidemiology Research Process

45 © 2004 Aeras Global TB Vaccine Foundation 45 What Determines What Data Are Collected? The research question! What data need to be collected is based on what you want to know. What data need to be collected is based on what you want to know. The study design outlines the primary end points and key data elements that indicate what data are needed. The study design outlines the primary end points and key data elements that indicate what data are needed.

46 © 2004 Aeras Global TB Vaccine Foundation 46 How Are Data Collected? Interviews & Questionnaires: Staff ask participants, doctors, participant families or others specific questions about participant health. Interviews & Questionnaires: Staff ask participants, doctors, participant families or others specific questions about participant health. Surveillance of Records: Staff review existing health records for specific health information related to participants. Surveillance of Records: Staff review existing health records for specific health information related to participants. Lab Tests: Staff conduct specific tests to gather information about participant health. Lab Tests: Staff conduct specific tests to gather information about participant health.

47 © 2004 Aeras Global TB Vaccine Foundation 47 Are All Data the Same? No! There are two types of data: Continuous Continuous Categorical Categorical

48 © 2004 Aeras Global TB Vaccine Foundation 48 Continuous Data Characteristics Based on a continuous scale of measurement, such as age, weight, and temperature. Based on a continuous scale of measurement, such as age, weight, and temperature. Not restricted to whole values and is measured rather than counted. Not restricted to whole values and is measured rather than counted. 4 weeks, 6 months, 1 year 3 months 4 weeks, 6 months, 1 year 3 months 19.1 kg, 20.7 kg, 27.3 kg 19.1 kg, 20.7 kg, 27.3 kg 98.7°, 101.3°, ° 98.7°, 101.3°, °

49 © 2004 Aeras Global TB Vaccine Foundation 49 Categorical Data Characteristics Data with two or more exclusive categories that are counted rather than measured. Data with two or more exclusive categories that are counted rather than measured. Data evaluated by sorting values into various categories. Data evaluated by sorting values into various categories. positive/negative positive/negative severe/moderate/mild severe/moderate/mild smoker/non-smoker smoker/non-smoker

50 © 2004 Aeras Global TB Vaccine Foundation 50 Activity: What type of data are the following?

51 © 2004 Aeras Global TB Vaccine Foundation 51 Continuous or Categorical? 39° Celsius 39° Celsius 4 years old 4 years old Severe Severe 185 centimeters 185 centimeters Male Male millimeters 16.5 millimeters Married Married Not-pregnant Not-pregnant 37% 37% 23% 23% Smoker Smoker Rating=4 Rating=4 4.1 inches 4.1 inches

52 © 2004 Aeras Global TB Vaccine Foundation 52 State the research question & formulate hypothesis. State in detail the question to be answered. State the research question & formulate hypothesis. State in detail the question to be answered. Choose the appropriate Study Design. Decide the best way to answer research question. Choose the appropriate Study Design. Decide the best way to answer research question. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Analyze the data. Analyze the data. Use biostatistics to examine data. Report your findings. Share what you learn so findings can be used to improve public health. Report your findings. Share what you learn so findings can be used to improve public health. Epidemiology Research Process

53 © 2004 Aeras Global TB Vaccine Foundation 53 Analyze Data Using Biostatistics Biostatistics is statistics applied to biological or medical information. Biostatistics is statistics applied to biological or medical information. Biostatistics applied to clinical research provides tools to compare and analyze outcome measures from collected data. Biostatistics applied to clinical research provides tools to compare and analyze outcome measures from collected data.

54 © 2004 Aeras Global TB Vaccine Foundation 54 How is Biostatistics Used? Summarize data so you can characterize groups. Summarize data so you can characterize groups. Compare results from two groups so that you can check for any differences. Compare results from two groups so that you can check for any differences. Looks for trends in the data. Looks for trends in the data.

55 © 2004 Aeras Global TB Vaccine Foundation 55 Ways to Summarize Data Counts – The total number counted. Counts – The total number counted. Number of cases Number of cases Proportions – The relationship between a population and a sub-sample of the population. Proportions – The relationship between a population and a sub-sample of the population. Number of cases per 100,000 Number of cases per 100,000 Number of cases per total population Number of cases per total population Rates - an expression of frequency, generally relative to a time unit. Rates - an expression of frequency, generally relative to a time unit. Kilometers per hour Kilometers per hour Number of cases per year Number of cases per year

56 © 2004 Aeras Global TB Vaccine Foundation 56 How Do You Tell the Difference? Counts are whole numbers. Counts are whole numbers. 1, 2, 3, etc 1, 2, 3, etc Proportions are comparisons of a subset to the whole. Proportions are comparisons of a subset to the whole. # per 100,000, 50%, etc. # per 100,000, 50%, etc. Rates have a time component. Rates have a time component. # per year, # per hour, # per month, etc. # per year, # per hour, # per month, etc.

57 © 2004 Aeras Global TB Vaccine Foundation 57 What Are the Two Types of Data Again? Continuous – Data based on a continuous scale of measurement, such as age, weight, and temperature. Continuous – Data based on a continuous scale of measurement, such as age, weight, and temperature. Categorical – Data with two or more exclusive categories that are counted rather than measured. Categorical – Data with two or more exclusive categories that are counted rather than measured.

58 © 2004 Aeras Global TB Vaccine Foundation 58 There are special methods for summarizing data, depending on the type of data you are working with. There are special methods for summarizing data, depending on the type of data you are working with. Depending the question to be answered, these measures of central tendency can help analyze data: Depending the question to be answered, these measures of central tendency can help analyze data: Summarize Continuous Data Mode Mode Median Median Mean Mean

59 © 2004 Aeras Global TB Vaccine Foundation 59 Referred to as the average. Referred to as the average. The arithmetic average in a set of values. The arithmetic average in a set of values. It is calculated by adding together all the individual values in a group of measurements and dividing by the number of values in the group. It is calculated by adding together all the individual values in a group of measurements and dividing by the number of values in the group = 28 ÷ 6 = 4.67 The Mean Is…

60 © 2004 Aeras Global TB Vaccine Foundation 60 A measure that divides a set of data into two equal parts. A measure that divides a set of data into two equal parts. For a set of values arranged in order of magnitude… For a set of values arranged in order of magnitude… the median is the middle value (for odd numbers of values) the median is the middle value (for odd numbers of values) the average of the two middle values (for an even number of values). the average of the two middle values (for an even number of values). The Median Is… : median = : median = 6.5

61 © 2004 Aeras Global TB Vaccine Foundation 61 The value that occurs most often in a set of values. The value that occurs most often in a set of values. The Mode Is… mode = mode = mode = 2 and 7

62 © 2004 Aeras Global TB Vaccine Foundation 62 State the research question & formulate hypothesis. State in detail the question to be answered. State the research question & formulate hypothesis. State in detail the question to be answered. Choose the appropriate Study Design. Decide the best way to answer research question. Choose the appropriate Study Design. Decide the best way to answer research question. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Do research & collect data. Conduct investigations as appropriate for the study design and record all the information specified. Analyze the data. Analyze the data. Use biostatistics to examine data. Report your findings. Share what you learn so findings can be used to improve public health. Report your findings. Share what you learn so findings can be used to improve public health. Epidemiology Research Process

63 © 2004 Aeras Global TB Vaccine Foundation 63 Review Descriptive epidemiology monitors disease in a community. Descriptive epidemiology monitors disease in a community. Analytic epidemiology answers questions about factors surrounding disease. Analytic epidemiology answers questions about factors surrounding disease. Three main study designs are: Three main study designs are: Retrospective (past) Retrospective (past) Cross-sectional (present) Cross-sectional (present) Prospective (future) Prospective (future)

64 © 2004 Aeras Global TB Vaccine Foundation 64 Review The study question or hypothesis determines: The study question or hypothesis determines: Study design. Study design. Data collected. Data collected. Bias is any effect that tends to produce results that depart systematically from true values. Bias is any effect that tends to produce results that depart systematically from true values. The two types of bias are selection bias and misclassification bias. The two types of bias are selection bias and misclassification bias.

65 © 2004 Aeras Global TB Vaccine Foundation 65 Review Randomization and blinding are strategies that minimize bias and ensure valid results. Randomization and blinding are strategies that minimize bias and ensure valid results. Active follow-up is when contact is made with all individuals in a study group to check for changes in status at particular points in time. Active follow-up is when contact is made with all individuals in a study group to check for changes in status at particular points in time. The advantage of active follow-up is that it results in relatively accurate reporting. The advantage of active follow-up is that it results in relatively accurate reporting.

66 © 2004 Aeras Global TB Vaccine Foundation 66 Review Passive follow-up is when no contact is made with individuals in a study group. Changes in status are detected by searching health records. Passive follow-up is when no contact is made with individuals in a study group. Changes in status are detected by searching health records. An advantage of passive follow-up is that it is relatively cheap and easy to do. An advantage of passive follow-up is that it is relatively cheap and easy to do. A sample is a subset of the target population. A sample is a subset of the target population.

67 © 2004 Aeras Global TB Vaccine Foundation 67 Review Sampling allows one to draw conclusions about the target population without including the entire population in the study. Sampling allows one to draw conclusions about the target population without including the entire population in the study. Five common outcome measures are: Five common outcome measures are: Mortality Mortality Morbidity Morbidity Prevalence Prevalence Incidence Incidence Change in physiological outcome Change in physiological outcome

68 © 2004 Aeras Global TB Vaccine Foundation 68 Review Data can be collected by: Data can be collected by: Interview Interview Surveillance Surveillance Lab tests Lab tests Continuous data is based on an uninterrupted scale of measurement. Continuous data is based on an uninterrupted scale of measurement. Categorical data has two or more exclusive categories that are counted rather than measured. Categorical data has two or more exclusive categories that are counted rather than measured.

69 © 2004 Aeras Global TB Vaccine Foundation 69 Review Biostatistics is a branch of statistics applied to clinical research. It provides tools to compare and analyze outcome measures. Biostatistics is a branch of statistics applied to clinical research. It provides tools to compare and analyze outcome measures. Counts capture the total number counted. Counts capture the total number counted. Proportions compare one part to another part or whole. Proportions compare one part to another part or whole. Rates show the frequency relative to a unit of time. Rates show the frequency relative to a unit of time.

70 © 2004 Aeras Global TB Vaccine Foundation 70 Review The mean is the average calculated by the sum of the values divided by the number of values in the group. The mean is the average calculated by the sum of the values divided by the number of values in the group. The median is the middle value in a set of values listed in sequence. The median is the middle value in a set of values listed in sequence. The mode is the value that occurs most often in a set of values. The mode is the value that occurs most often in a set of values. Mean, median and mode summarize continuous data. Mean, median and mode summarize continuous data.

71 © 2004 Aeras Global TB Vaccine Foundation 71 Epidemiology & Biostatistics 2 This presentation is produced by Aeras Global TB Vaccine Foundation SM in collaboration with the University of Cape Town and the South African Tuberculosis Vaccine Initiative. A special thanks to Greg Hussey F.S.C.H., Tony Hawkridge, F.C.P.H.M., Hassan Mahomed, M. Med, Marie Buchanan, Marijke Geldenhuys, MSHS CRA, Marwou De Kock, B.Tec., Sylvia Silver, D.A., Jen Page, M.Ed. Larry Geiter, Ph.D., and Peggy Goetz, M.P.H., for their contributions and support for this presentation.


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