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Teacher Note: Module 2 Overview Content Area: Hypothesis-Testing: Cross-Sectional Study

Teacher Note: Module 2 Overview Content Area: Hypothesis-Testing: Cross-Sectional Study

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Teacher Note: Module 2 Overview Content Area: Hypothesis-Testing: Cross-Sectional Study

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  1. Teacher Note: Module 2 Overview Content Area: Hypothesis-Testing: Cross-Sectional Study Essential Questions: How can I select groups of people and collect data/evidence from them that will test my hypothesis? If my causal hypothesis is correct, how would the exposure and outcome be distributed in these groups? Enduring Understanding: Causal hypotheses can be tested by conducting investigations of the exposures and outcomes of selected groups of people as they go about their lives. Information from these observational studies can be used to determine if an exposure and an outcome are associated. Because observational studies are complicated by factors not controlled by the observer, when an association is found, other explanations in addition to causality also must be considered. • Core Concepts: • Testing hypotheses • Association • Exposure/outcome • Comparison group • 2x2 table • Observational studies • Study design/study plan • Study samples • Prevalence rate • Prevalence ratio • Statement of effect Lessons: 2-1 Looking for Associations 2-2 Cross-Sectional Studies 2-3 Developing Hypothesis and Study Questions 2-4 Respect – Part II 2-5 Planning Study Conduct 2-6 Cross-Sectional Study - In Class 2-7 Cross-Sectional Study – In School Revised Sept 14, 2011

  2. Teacher Note: Enduring Epidemiological Understandings for the Epidemiology and the Energy Balance Equation Curriculum Health and disease are not distributed haphazardly in a population. There are patterns to their occurrence that can be identified through surveillance. Analysis of the patterns of health and disease distribution can provide clues for formulating hypotheses about their possible causes. Causal hypotheses can be tested by conducting investigations of the exposures and outcomes of selected groups of people as they go about their lives. Information from these observational studies can be used to determine if an exposure and an outcome are associated. Because observational studies are complicated by factors not controlled by the observer, other explanations also must be considered.

  3. Teacher Note: Authentic Assessment for Module 2 of the Epidemiology and the Energy Balance Equation Curriculum Students will conduct, analyze, and interpret observational, cross-sectional studies among students in their class and then among students outside their class. Working in teams, students will have the opportunity to demonstrate their abilities to select a reasonable hypothesis of interest to them, design study questions about exposure and outcome, obtain informed consent, collect and manage data, calculate and compare prevalence rates, make accurate statements about whether their data support that hypothesis, and consider alternate explanations for what they observed. Reporting of results will be required, such as a written report, an item for the school newspaper, or an oral presentation or poster for students, teachers, and/or parents. Specific performance criteria will be used to help ensure that the experiences allow a genuine, realistic, and fair assessment of students’ comprehension of the Module 2 Enduring Epidemiological Understanding.

  4. Start of Lesson 2-2 (estimate 1 class period)

  5. Review • Big Ideas in Lesson 2-1 • Two things are associated when they “turn up together” • Epidemiologists study associations. • Descriptive epidemiology generates hypotheses about associations • Analytical epidemiology tests hypotheses about associations • A common way to test hypotheses is with an observational study of a natural experiment • The 2x2 table is a useful tool for numerically expressing associations between exposure and outcome in a group of individuals

  6. The Journey from Exposure to Outcome

  7. Main Types of Analytical Epidemiology Studies EXPERIMENTAL Manipulates who is exposed and the exposure dose Controlled Trial Quasi-Experiment OBSERVATIONAL Studies natural experiments Cohort Study Case-Control Study Cross-Sectional Study

  8. No Outcome Outcome Total Exposed Not Exposed IMPORTANT NOTICE! Remember that any of the study types can use the idea of a 2x2 table to explore a possible association between and exposure and an outcome

  9. Cross-Sectional Study Sometimes called a prevalence study A snapshot of what is going on One point in time An observational study

  10. What Do You Think? • Would the quickest and easiest study be experimental or observational? • Observational • What would be the least amount of data you could collect from each study participant [in order to study an association]? • Two questions – one about the exposure, and one about the outcome

  11. Hypothesis: Students Who Bring Their Lunch From Home Are Likely To Eat More Fruits and Vegetables What is the exposure in this hypothesis? What is the outcome in this hypothesis?

  12. Using Data From a Real Cross-Sectional Study

  13. Hypothesis: Students Who Bring Their Lunch From Home Are Likely To Eat More Fruits and Vegetables <5 servings of fruits and vegetables per day 5 or more servings of fruits and vegetables per day Total Bring lunch from home 4-5 days per week 339 718 379

  14. Outcome Review as Needed - Concepts of Prevalence The numerator is the number of people in the population or sample who experienced the outcome. The denominator is the total number of people in the population or sample. Population / Sample

  15. CHIS study - Express It In Numbers + Numerator Students who bring their lunch to school from home 4-5 days per week AND eat 5 or more servings of fruits and vegetables per day Denominator All students who bring their lunch to school from home 4-5 days per week

  16. 47% or Hypothesis: Students Who Bring Their Lunch From Home Are Likely To Eat More Fruits and Vegetables Tested Prevalence Rate of eating 5 or more servings per day <5 servings of fruits and vegetables per day 5 or more servings of fruits and vegetables per day Total Bring lunch from home 4-5 days per week 339 718 339 718 379

  17. Inference Process of predicting from what is observed in a sample, to what is true for the entire population.

  18. 47% or Hypothesis: Students Who Bring Their Lunch From Home Are Likely To Eat More Fruits and Vegetables <5 servings of fruits and vegetables per day 5 or more servings of fruits and vegetables per day Prevalence Rate of eating 5 or more servings per day Total NOTHING! Bring lunch from home 4-5 days per week 339 379 718 339 718 What does this tell you about the hypothesis?

  19. 47% or Hypothesis: Students Who Bring Their Lunch From Home Are Likely To Eat More Fruits and Vegetables TestedPrevalence Rate of eating 5 or more servings per day <5 servings of fruits and vegetables per day 5 or more servings of fruits and vegetables per day Total 339 Bring lunch from home 4-5 days per week 379 718 339 718 To study an association between an exposure and an outcome, we need to compare prevalence of the outcome among people with the exposure to prevalence of the outcome among people without the exposure.

  20. Definition of a Comparison Group People who are observed in a study but do not have the exposure People whose results are compared to the group that has the exposure

  21. 47% or Including a Comparison Group Prevalence Prevalence of eating 5 or more servings per day Total 339 339 379 718 718 a b c d ? ? % or ? Extend and label the table to include a comparison group.

  22. 47% or Including a Comparison Group 5 or more servings of fruits and vegetables per day Prevalence Prevalence of eating 5 or more servings per day <5 servings of fruits and vegetables per day Total 339 Bring lunch from home 4-5 days per week 339 379 718 718 a b c d ? ? % or ? ?

  23. Who would you choose as the comparison group?

  24. 47% or ? ? % or 1,479 Including a Comparison Group 5 or more servings of fruits and vegetables per day Prevalence Prevalence of eating 5 or more servings per day <5 servings of fruits and vegetables per day Total 339 Bring lunch from home 4-5 days per week 339 379 718 718 a b c d Never bring lunch from home 1,479 “Never bringing lunch from home “ can mean eating in the school cafeteria or away from school, or not eating lunch at all

  25. 47% or Results of Actual Study 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence of eating 5 or more servings per day Total Bring lunch from home 4-5 days per week 339 339 379 718 718 a b c d Never bring lunch from home 1,479 526 953

  26. 47% or Results of Actual Study 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence of eating 5 or more servings per day Total 339 Bring lunch from home 4-5 days per week 339 379 718 718 a b c d 526 Never bring lunch from home 36% or 1,479 526 953 1,479

  27. Actual Study Results Prevalence and Prevalence Ratio Prevalence Prevalence of eating 5 or more servings per day 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence Ratio Total 339 Bring lunch from home 4-5 days per week or 47% 339 379 718 718 1.31 a b c d Never bring lunch from home 526 526 953 1,479 or 36% 1,479

  28. Actual Study Results Prevalence and Prevalence Ratio 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence of eating 5 or more servings per day Prevalence Ratio Total Bring lunch from home 4-5 days per week 339 or 47% 339 379 718 718 1.31 a b c d Never bring lunch from home 526 526 953 1,479 or 36% 1,479 1.3 Students who bring their lunch from home 4-5 days per week are _____ times as likely to eat 5 or more servings of fruits and vegetables compared to students who never bring their lunch from home.

  29. Interpretation of Prevalence Ratios

  30. What if comparison numbers had been different? Hypothetical Analysis # 1 Prevalence Prevalence of eating 5 or more servings per day 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence Ratio Total 339 Bring lunch from home 4-5 days per week or 47% 339 379 718 718 1.00 a b c d Never bring lunch from home 695 695 784 1,479 or 47% 1,479 Students who bring their lunch from home 4-5 days per week are 1.0 times as likely to eat 5 or more servings of fruits and vegetables compared to students who never bring their lunch from home.

  31. Interpretation of Prevalence Ratios

  32. What if comparison numbers had been different? Hypothetical Analysis # 2 Prevalence Prevalence of eating 5 or more servings per day 5 or more servings of fruits and vegetables per day <5 servings of fruits and vegetables per day Prevalence Ratio Total 339 Bring lunch from home 4-5 days per week or 47% 339 379 718 718 0.70 a b c d Never bring lunch from home 1,010 1,035 444 1,479 or 67% 1,479 Students who bring their lunch from home 4-5 days per week are0.70 times as likely to eat 5 or more servings of fruits and vegetables compared to students who never bring their lunch from home.

  33. Interpretation of Prevalence Ratios These examples show how prevalence ratios are impacted by the prevalence rate in the comparison group. Without this information, the prevalence ratio of the exposed group is not interpretable.

  34. Egg Chicken Another Issue in Interpretation: Which came first?

  35. Re-Cap of Big Ideas So Far . . . • Big Ideas in Lesson 2-2 • The cross-sectional design is an observational • study of a natural experiment • This design is relatively quick and simple, • asking individuals about exposure and outcome at one point in time • When prevalence is calculated for the group with the exposure, the next question is “compared to what?” • The “compared to what” consists of prevalence for the unexposed comparison group • Dividing one prevalence by the other produces the prevalence ratio; it tells us if/how the exposure and outcome are associated • Because exposure and outcome are measured at the same point in time, it is usually not possible to determine the time order of the exposure and the outcome (which came first) and as such, the association may not be interpretable

  36. Optional session to explore how a real study is reported (the CHIS example)

  37. How is a real study reported? OPTIONAL – may be best suited for high school Theresa A. Hastert, Susan H. Babey. School lunch source and adolescent dietary behavior. Prevention of Chronic Diseases 2009; Vol 6 (4) http://www.cdc.gov/pcd/issues/2009/oct/08_0182.htm

  38. Methods • “We analyzed cross-sectional data for 2,774 adolescents who responded to the 2005 California Health Interview Survey (CHIS) and reported dietary behaviors for a weekday.” • Identify key information about the study presented in this single-sentence description of the methods. What study design was used? What was the sample size? Who were the study subjects? When did the survey take place? What was the name of the survey? What topic was being studied?

  39. Results “In bivariate analyses, adolescents who typically brought their lunch from home 5 days per week ate fast food on fewer occasions; consumed fewer servings of soda, fried potatoes, and high-sugar foods; and ate more fruit and vegetables compared with adolescents who never brought their lunch to school.In linear regressions controlling for demographics, body mass index, desire to change weight, parent education, and adult presence after school, students who typically brought their lunch to school 5 days per week ate fast food 0.35 fewer times and consumed 0.35 fewer servings of soda, 0.10 fewer servings of fried potatoes, 0.25 fewer servings of high-sugar foods, and 0.95 more servings of fruit and vegetables per day compared with students who never brought their lunch to school.”

  40. Results “In bivariate analyses, adolescents who typically brought their lunch from home 5 days per week ate fast food on fewer occasions; consumed fewer servings of soda, fried potatoes, and high-sugar foods; and ate more fruit and vegetables compared with adolescents who never brought their lunch to school.In linear regressions controlling for demographics, body mass index, desire to change weight, parent education, and adult presence after school, students who typically brought their lunch to school 5 days per weekate fast food 0.35 fewer times and consumed 0.35 fewer servings of soda, 0.10 fewer servings of fried potatoes, 0.25 fewer servings of high-sugar foods, and 0.95 more servings of fruit and vegetables per day compared with students who never brought their lunch to school.”

  41. Results “In bivariate analyses, adolescents who typically brought their lunch from home 5 days per weekate fast food on fewer occasions; consumed fewer servings of soda, fried potatoes, and high-sugar foods; and ate more fruit and vegetables compared with adolescents who never brought their lunch to school. In linear regressions controlling for demographics, body mass index, desire to change weight, parent education, and adult presence after school, students who typically brought their lunch to school 5 days per week ate fast food 0.35 fewer times and consumed 0.35 fewer servings of soda, 0.10 fewer servings of fried potatoes, 0.25 fewer servings of high-sugar foods, and 0.95 more servings of fruit and vegetables per daycompared with students who never brought their lunch to school.”

  42. Table 2. Dietary Intake as a Function of Days Bringing Lunch to School Among California Adolescents Aged 12-17 Years, California Health Interview Survey, 2005

  43. Table 2. Dietary Intake as a Function of Days Bringing Lunch to School Among California Adolescents Aged 12-17 Years, California Health Interview Survey, 2005

  44. Table 2. Dietary Intake as a Function of Days Bringing Lunch to School Among California Adolescents Aged 12-17 Years, California Health Interview Survey, 2005

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