Review – First Exam Chapters 1 through 5 Review questions at the end of the chapters are good Focus on Key Concepts Don’t need to know specifics from Chapter 4 which includes information on sources of public health data. Exam 10/04 and review is 9/27 Project Question and Aim due 10/2

Overview of Epidemiologic Study Designs

Questions to Ask Exposure  Outcome How should you define your exposure(s)? In which people? How should you define your disease? How can you make your study accurate? Bias Confounding Random error How can you make your study efficient? Time Money

Experimental Study Purpose Key Feature Setting Study preventions and treatments for diseases. Key Feature Investigator assigns individuals to two or more groups that either do or do not receive a preventive or therapeutic agent and follows the groups for incidence of outcome. Setting Ethical and feasible Able to detect even a small effect Money is available – most expensive study design

Cohort Study Purpose Key Feature causes preventions treatments Subjects selected based on exposure Followed for disease occurrence

Cohort Study Setting Trial not ethical, feasible, or too expensive Moderate or large effect expected Little known about exposure and so can evaluate many effects of an exposure Exposure is rare Underlying population is fixed

Cross-Sectional Study Purpose Descriptive, prevalence Associations Key Feature Random sample of a population, or weighted sample Single time point

Cross-Sectional Study Setting Initial/early study of exposure  outcome relationship Descriptive information needed Trial not ethical, feasible, or too expensive. Moderate or large effect expected. Little known about exposure or outcome. Neither exposure or outcome is too rare.

Case-Control Study Purpose Key Feature Studies causes Preventions and treatments for diseases. Key Feature Sample based on case-control status CASE – Method of sampling cases. CONTROL – source population that gave rise to the cases (controls) Compare exposure distribution in cases and controls

Case-Control Study Setting Trial not ethical, feasible, or too expensive. Moderate or large effect expected. Little known about disease and so can evaluate many exposures. Disease is rare. Underlying population is dynamic.

Ecologic Study Purpose Key Features Very early stage of investigating exposure  outcome Key Features Unit of analysis is at the level of the group level Example – per capita sugar consumption per country and incident rates of diabetes

Which type of design is being described in each of the following scenarios? A study that evaluates the relationship between breast cancer and a woman’s history of breast feeding. The investigator selects women with breast cancer and an age-matched sample of women who live in the same neighborhoods as the women with breast cancer. Study subjects are interviewed to determine if they breastfed any of their children.

Which type of design is being described in each of the following scenarios? A study that evaluates two treatments for breast cancer. Women with stage 1 breast cancer are randomized to receive either lumpectomy alone or lumpectomy with breast radiation. Women are followed for five years to determine if there are any differences in breast cancer recurrence and survival.

Which type of design is being described in each of the following scenarios? A study of the relationship between exposure to chest irradiation and subsequent risk of breast cancer that was begun in 2005. In this study, women who received radiation therapy for post-partum mastitis in the 1940s were compared to women who received a non-radiation therapy for post-partum mastitis in the 1940s. The women were followed until 2001 to determine the incidence rates of breast cancer in each group.

Which type of design is being described in each of the following scenarios? A study of the relationship between exposure to postmenopausal hormone therapy and subsequent risk of breast cancer that will begin in January 2013. In this study, postmenopausal women who receive hormone therapy during 2013 will be compared to postmenopausal women who do not receive this therapy. The women will be followed until 2023 to determine the incidence rates of breast cancer in each group.

Which type of design is being described in each of the following scenarios? A study that examines the death rates from colon cancer in each of the 50 US states in relation to the average percentage of residents in each state undergoing colonoscopy screening.

What type of study would you use for: Identifying causes of a rare disease Identifying the long term effects of a rare exposure Studying the health effects of an exposure for which information is difficult and expensive to obtain Identifying the causes of a new disease about which little is known Identifying the short-term health effects of a new exposure about which little is known. Identifying the causes of a disease with a long latent period.

True or False Observational studies of preventions and treatments are often conducted when experimental studies are unethical or infeasible. The main limitation of observational studies is the investigators inability to have complete control of extraneous factors called confounders. A cross-sectional study of the relationship between blood type and the risk of cataracts will produce misleading results because you cannot tell the correct temporal relationship between the exposure (blood type) and disease (cataracts).

True or False An ecological study was done to determine the relationship between per capita soft drink consumption and mortality rates from diabetes in 10 US states. The investigators found a strong association between soft drink consumption an diabetes mortality. Based on this study, we can conclude that the individual who consumed the soft drinks were the ones who died from diabetes. Case-control studies are inherently inferior to cohort studies. Experimental studies are inherently superior to observational studies.

State the main difference between these types of studies. Observational and experimental studies. Retrospective and prospective cohort studies. Cohort and case-control studies.

Considerations for Choosing a Particular Design Research question Existing scientific knowledge Frequency of exposure and disease Ethical considerations Concerns about validity, random error, efficiency

Which study design to choose? In theory, it's possible to use all three designs to test a hypothesis. What are the issues in using a case-control study design? What are the issues in using a cohort study design? What are the issues in using an randomized clinical trial?

Case- Control Study E E Determines and Compares Cases of Lung Cancer E Determines and Compares Past Vitamin A Consumption Source Population Investigator Selects E Controls =sample of source pop

Determines and Compares Lung Cancer Incidence Cohort Study D High Vitamin A Group Determines and Compares Lung Cancer Incidence Source Population Investigator Selects Time Passes D Low Vitamin A Group

Determines and Compares Lung Cancer Incidence Experimental Study High Vitamin A Group Determines and Compares Lung Cancer Incidence Source Population Time Passes Investigator Assigns D Low Vitamin A Group

Summary Choice of study designs balances many considerations… Research question Existing scientific knowledge Frequency of exposure and disease Ethical considerations Concerns about validity, random error, efficiency Efficiency – cost and time Each design has complementary strengths and weaknesses

Research Proposal Research Question Hypothesis Null – no association Alternative – an association, but no direction Research/Operational – indicate direction Cross-sectional surveys can have hypotheses

Research Question Hypothesis Hypothesis Example Null – no association Alternative – an association, but no direction Research/Operational – indicate direction Cross-sectional surveys can have hypotheses Hypothesis Example Null – Obesity is not associated with diabetes. Alternative – Obesity is associated with diabetes. Research/Operational – Obese individuals have a higher risk of developing diabetes than non-obese individuals. Cross-sectional: Obese individuals are more likely than normal weight individuals to have diabetes.

Research Proposal – Background and Significance Section Magnitude of the problem – why do we care Prevalence in the US or SC Outcome Exposure Strengths – unique and novel aspects Population available Exposure measurement Outcome measurement Therefore, we propose to study X here Background and Significance (include 4 to 8 references and use endnote for the references)

Key Components -- Study Feasible – it must be possible to answer the question analytically (scientifically, time, resources) Interesting – the question should generate interest among the consumers of the research Novel – the question should add something new to the field of research Ethical – procedures needed to answer the question must not compromise the protection of human subjects Relevant – the question should address issues that are timely, have an impact on the study population, and make a contribution to the field of study