Study Design Descriptive Studies

Descriptive Studies Descriptive studies often represent the first scientific toe in the water in new areas of inquiry. A fundamental element of descriptive reporting is a clear, specific, and measurable definition of the disease or condition in question. Like newspapers, good descriptive reporting answers the five basic W questions: who, what, why, when, where . . . and a sixth: so what?

Descriptive Studies Case reports, case-series reports, cross-sectional studies, and community surveys deal with individuals, whereas ecological correlational studies examine populations.

Community Survey A community survey is a study which attempts to ascertain the frequency of a disease in a fixed geographic region (ideally) or in a group defined by a common membership, e.g. school-children. It usually assesses the frequency of disease in easily ascertained sub-groups, i.e. age, gender, geographic sub-units, ethnicity etc. It is often the first step in looking at risk factors for disease.

Community Survey An example of a community survey is the EuroPrevall study. Researchers will ask 30,000 children from 10 European countries about symptoms that may be related to food allergy using a questionnaire. The researchers will identify adults for the study by using lists of patients from general practitioners. When the results of these studies are available in a few years’ time, there will be a much clearer picture of the true percentage of people with food allergy in the general population and the differences that may exist across Europe.

Case Series/Case Report Consist of collections of reports or one report on the treatment of individual patients or a report on a single patient. Because they are reports of cases and use no control groups to compare outcomes, they have little statistical validity. The case report is the least-publishable unit in medical literature. Case-series reports aggregate individual cases in one publication.

Case Series/Case Report Clustering of unusual cases in a short period often heralds a new epidemic, as happened with AIDS. These are observational, but the observation might, with further studies over time, prove to be invalid. But, inquiry has to start somewhere.

Case Series/Case Report For example, just looking at this picture, you conclude that books can fly.

Case Series/Case Report From: Suny Downstate Medical Center, Evidence Based Medicine Tutorial, http://library.downstate.edu/EBM2/2600.htm

Cross-Sectional Study A cross-sectional study is a type of observational research that analyzes and compares populations without manipulating variables within the study environment. Researchers carry out cross-sectional studies over a specific point in time.

Cross Sectional Study Cross-sectional studies can be descriptive or analytical. A cross-sectional survey may be purely descriptive and used to assess the burden of a particular disease in a defined population. For example a random sample of schools across Atlanta may be used to assess the prevalence of asthma among 12-14 year olds.

Cross-Sectional Study Prevalence can be assessed at either one point in time (point prevalence) or over a defined period of time (period prevalence). Period prevalence is required when it takes time to accumulate sufficient information on a disease in a population, e.g. what proportion of persons served by a public health clinic over a year have hypertension.

Cross Sectional Study From: Study.com, Cross-Sectional Research: Definition & Examples, http://study.com/academy/lesson/cross-sectional-research-definition-examples-quiz.html

Ecological Study Ecological correlational studies look for associations between exposures and outcomes in populations—eg, per capita cigarette sales and rates of coronary artery disease—rather than in individuals.

Ecological Study From: Boston University School of Public Health, http://sphweb.bumc.bu.edu/otlt/MPH-Modules/QuantCore/PH717_DescriptiveStudies/PH717_DescriptiveStudies7.html

Question You want to know if the prevalence of breast cancer increases with age. You look at three groups of women who are similar but of different ages -- 20-35 years, 36-50 years, and 51-65 years. You then calculate the percentage of women in each group that have been diagnosed with breast cancer. Which of the following correctly identifies the study design you used? Case-Report Case Series Cross Sectional Study Ecological Study

Answer Cross-Sectional Study Cross-sectional research involves using different groups of people who differ in the variable of interest but share other characteristics, such as socioeconomic status, educational background, and ethnicity.

Question A physician treated a young and otherwise healthy patient who came to her office reporting numbness all over her body. The physician could not determine any reason for this numbness and had never seen anything like it. After taking an extensive history the physician discovered that the patient had recently been to the beach for a vacation and had used a very new type of spray sunscreen. The patient had stored the sunscreen in her cooler at the beach because she liked the feel of the cool spray in the hot sun. The physician suspected that the spray sunscreen had undergone a chemical reaction from the coldness which caused the numbness. She also suspected that because this is a new type of sunscreen other physicians may soon be seeing patients with this numbness, she wrote an article about it. Which of the following correctly identifies the study design you used? Case Report Case Series Cross Sectional Study Ecological Study

Answer Case Report A Case Report is an article that describes and interprets an individual case, often written in the form of a detailed story.