Module 2 – SLP
DESCRIPTIVE AND ANALYTIC EPIDEMIOLOGY
Designing an Epidemiologic Study to Test the Hypothesis
To test the hypothesis on the source of the outbreak, a case-control study was conducted from July 21-27. Thirty-one of the initial 38 persons meeting the original case definition (i.e., those not used in hypothesis-generating interviews) were included as cases. It was decided that two controls would be selected for every case and would be matched to the case by age group (0-<2 years, 2-<5 years, 5-<12 years, 12-<18 years, 18-<60 years, and 60+ years) and gender.
The investigators identified controls for the study using sequential digit dialing. Exposure information among cases was collected for the 7 days before onset of illness. For controls, exposure information was collected for the 7 days before the interview and for the 7 days before the onset of illness in the matching case.
Twenty-seven case-control sets were interviewed; the remaining case-patients could not be reached.
Session Long Project
Please answer these questions:
- How would you define controls for this study? What methods might be used to identify controls?
- Do you agree with the investigators’ decision to match on age group and gender? Why or why not?
- Over what time period would you examine exposures to possible risk factors for cases? For controls?
SLP Assignment Expectations
Length: SLP assignments should be at least 4 pages (1000 words) in length.
Assessment and Grading: Your paper will be assessed based on the performance assessment rubric that is linked within the course. Review it before you begin working on the assignment. Your work should adhere to these MSHS Assignment Expectations.
Module 2 – Home
DESCRIPTIVE AND ANALYTIC EPIDEMIOLOGY
Modular Learning Outcomes
Upon successful completion of this module, the student will be able to satisfy the following outcomes:
- Case
- Make inferences regarding the pattern of disease.
- Describe a disease by person, place, time, and magnitude.
- SLP
- Describe key methodological considerations for a case-control study, including definitions and methods for identifying controls and time frame for study.
- Discussion
- Make inferences using descriptive epidemiology.
Module Overview
Descriptive epidemiology is defined as the study of the amount and distribution of disease within a population by person, place, and time. Descriptive epidemiology answers the following questions: Who is affected? Where and when do cases occur? It describes cases by person, place, and time.
Person
In epidemiologic studies, there are many characteristics that may be used to describe the affected population. These characteristics include age, sex, ethnic group or race, social class, occupation, marital status, family variables, blood type, environmental exposures, and personality traits. Among these characteristics, the most commonly used are age, sex, and ethnic group or race. Age is the most important variable among the personal variables because of its effect on morbidity and mortality rates. In general, chronic conditions tend to increase with age, while the relation of age to acute infectious diseases is less consistent. Age is also related to the severity of infectious disease. For example, certain organisms such as Salmonella tend to produce severe disease in the very young, the very old, and the debilitated.
The analysis of disease rates by sex reveals a marked contrast between morbidity and mortality rates. Death rates are higher for males and females, but morbidity rates are generally higher in females. Possible explanations for this disparity are that women seek medical care more frequently and perhaps earlier in the stage of disease and that the same disease tends to have a less lethal course in women than in men.
Although the classification of disease by race or ethnicity has been controversial, it has been used traditionally in health statistics since many diseases differ considerably in frequency and severity for different racial groups. For example, whites have higher rates of death from arteriosclerotic heart disease, suicide, and leukemia, while African-Americans have higher rates of deaths caused by hypertensive heart disease, cerebrovascular accidents, tuberculosis, homicide, and accidental death.
Social class is a commonly used concept for ranking a population into subgroups that differ in prestige, wealth, and power. Epidemiologic data indicates an inverse relationship between mortality and social class. Because of practical considerations, occupation is often used alone as a measure of overall socioeconomic status. The poor health status of individuals in lower socioeconomic groups may be largely due to poverty. Because of limited financial resources and restricted access to medical care, the poor tend to underutilize preventive services.
Occupation can have a significant effect on morbidity and mortality rates since individuals spend a substantial part of their lives working in diverse conditions. These conditions may include unfavorable physical conditions (e.g., heat and cold), chemicals, noise, and occupationally induced stress. For example, air traffic controllers (who have unusually stressful working conditions because of the potentially disastrous effects of errors in judgment) have higher rates of hypertension and peptic ulcer. The rates of disease among occupational groups may also differ because of selective factors (differences that caused individuals to choose the occupation, rather than the work conditions).
Marital status has been related to the level of mortality for both sexes. Death rates have generally been lowest among the married and highest among the divorced. The lower mortality rates among the married may be attributed to psychological and physical support provided by the spouse, selective factors, and health differences in pregnancy and childbearing (which have been inversely associated with cervical and breast cancer).
Family variables that may be associated with mortality and morbidity rates include family size, birth order, maternal age, and parental deprivation. Larger families tend to be more common among the poor. Therefore, children may be at a disadvantage, especially since many persons must share a family’s limited resources. A variety of findings have indicated that firstborns, who tend to be more educated, have higher rates of asthma, peptic ulcer, and schizophrenia. Birth order may play a role in a person’s life experiences because firstborns tend to receive more attention than younger siblings. The maternal age (age of a mother at the time of childbirth) is associated with birth defects, which in turn, affect morbidity and mortality rates in their children. For example, the incidence rate of Down’s syndrome increases with maternal age. Parental deprivation (due to death, divorce, or separation) has been found to be high among individuals with psychiatric and psychosomatic disorders, individuals with tuberculosis, and those who have attempted suicide.
Analytic Epidemiology
Analytic epidemiology is defined as the study of the determinants of disease or reasons for relatively high or low frequency in specific groups. Analytic epidemiology answers questions regarding why the rate is high or low in a particular group. To identify reasons for high or low frequencies in specific groups, analytic studies are conducted. Review analytic studies by clicking on the button below:
Analytic studies are designed to determine whether an association exists between a factor (or exposure) and a disease, and if so, to determine the strength of an association. Measures of association will be further discussed in Module 4.
Case-Control Studies Studies in which the proportion of cases with a potential risk factor are compared to the proportion of controls (individuals without the disease) in terms of that risk factor. These studies are commonly used for initial, inexpensive evaluation of risk factors and are particularly useful for rare conditions or for risk factors with long induction periods.
For more information on case-control studies, go to Coggon, D., Rose, G., & Barker, D. J. P. (2007) Chapter 8: Case-control and cross sectional studies. In Epidemiology for the Uninitiated (4th edition). British Medical Journal. Available at: https://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated/8-case-control-and-cross-sectional
Module 2 – Background
DESCRIPTIVE AND ANALYTIC EPIDEMIOLOGY
Required Reading
Centers for Disease Control and Prevention. (2012). Lesson one: Introduction to epidemiology: Section 6: Descriptive epidemiology. In Principles of Epidemiology in Public Health Practice, 3rd Edition. Retrieved May 1, 2019, from https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section6.html
Centers for Disease Control and Prevention. (2012). Lesson one: Introduction to epidemiology: Section 7: Analytical epidemiology. Principles of Epidemiology in Public Health Practice, 3rd Edition. Retrieved May 1, 2019, from https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section7.html
Coggon, D., Rose, G., & Barker, D. J. P. (2007) Chapter 8: Case-control and cross sectional studies. In Epidemiology for the Uninitiated (4th edition). British Medical Journal. Retrieved on May 22, 2012, from http://www.bmj.com/about-bmj/resources-readers/publications/epidemiology-uninitiated
Herbert, R. (2017). Case-control studies. Journal of Physiotherapy, 63(4), 264-266. doi:10.1016/j.jphys.2017.08.007