Cohort Study

Introduction

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Learning Objectives

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Student Role

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Study Design

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Data Collection

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Data Analysis

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Discussion Questions

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Step 3: Study Design

From your studies, you know that the first step in any research plan is to generate a solid hypothesis to guide the investigation.So, while the WEPI1 newscast and Ms. Doll provided you with interesting information, you decide to visit a local hospital to inquire about individuals with Susser Syndrome.

Upon initial review of the cases, it does appear that a number of affected individuals did, in fact, work at the Glop Industries manufacturing plant. However, other individuals not associated with the factory have been affected as well (albeit in smaller numbers). You learn that Glop industries keeps meticulous information about its employees' work histories, which you decide to use in your study. With this exposure information from the employee records, you want to conduct a cohort study. Since both the exposure and outcome have already occurred, and since you have access to the exposure data collected prior to the disease outcome, you decide to design a retrospective cohort study (Please see Aschengrau pp. 151 and 198-200 for more information).

1.	Based on the facts as presented, which do you think is the best hypothesis to investigate in this retrospective cohort study?
		a.	Those who develop Susser Syndrome are more likely to have participated in the manufacturing of SUPERCLEAN than those who did not develop Susser Syndrome.
		b.	Those who are exposed to chemicals involved in the production of SUPERCLEAN (via direct exposure at the factory) have a higher risk of developing Susser Syndrome than those who are not exposed.
		c.	Residents of Epiville have a higher risk of developing Susser Syndrome compared with the residents of a neighboring community.

To simplify the study design, you decide to assemble a cohort in which all study participants enter into the study at the same time (September 1, two years ago); however, some study participants will be followed for less than two years.

2.	Based on your hypothesis, what would be the best way to define exposure?
		a.	Provide all workers at the Glop Industries manufacturing plant with individual air quality instruments to take daily readings in order to compile weekly doses of exposure to SUPERCLEAN.
		b.	Ask workers about their professional activities at the factory and estimate their exposure to SUPERCLEAN.
		c.	Look for sources of information at the factory which record individual worker exposures throughout their employment.

Your supervisor assembles a team to begin the investigation. After a little groundwork, you find that the employee health clinic at Glop Industries keeps records of annual medical examinations for all employees beginning with their hiring date. You also learn that the factory’s human resources department has records of each worker’s employment history which you can use to determine exposure to chemicals involved in the SUPERCLEAN production. Among the 40 job positions at the factory, only 5 are directly involved with the production of SUPERCLEAN.

After talking with some environmental experts and epidemiologists, you believe that an individual needs to have been exposed to SUPERCLEAN for at least 6 months before a sufficient dose of the chemical accumulates and physiological changes start taking place. Thus, exposure to SUPERCLEAN production chemicals for less than 6 months will not lead to Susser Syndrome.

You are presented with the job descriptions that are exposed to SUPERCLEAN and Glop Industries’ air monitoring records.

After some deliberation, you define the exposed groups as low, medium or high exposure (depending on the maximum allowable level of exposure to SUPERCLEAN for their job category) and the unexposed group as employees either not involved with SUPERCLEAN production or those working less than 6 months in SUPERCLEAN production.

You now have the basic framework of your retrospective cohort study. You have redefined your hypothesis to incorporate your assumptions about the induction period and you have clearly defined your exposure variable. You are obviously excited to get out there and begin collecting data but you must first determine who is eligible for the study.

3.	How would you define eligibility criteria for study participants? [Aschengrau p. 197 - 198]
		a.	Everyone working at the factory is eligible
		b.	Only those who have worked at the factory as of September 1, two years ago, AND had been on the job for at least 6 months AND who were shown to be healthy at their initial or annual health check-ups as indicated by employee medical records
		c.	Exclude workers who in the last three months exhibited symptoms of the disease

4.	On what would you base your definition of Susser Syndrome? [Aschengrau p. 209 - 211]
		a.	Neurological symptoms alone
		b.	Self-diagnosis of the participants
		c.	Combination of neurological symptoms and laboratory tests

Introduction

>

Learning Objectives

>

Student Role

>

Study Design

>

Data Collection

>

Data Analysis

>

Discussion Questions