Descriptive studies

Example L Kono (2004) conducted an ecological study in Japan that compared consumption of selected nutrients with annual colon cancer incidence and mortality across time. Annual per capita consumption data of selected nutrients and foods was obtained from nationwide surveys, which were conducted from 1950 to 2000 and contained data from randomly selected houses across the nation. The food group identified as meat contained poultry and fish. Consumption of red meat was not available for the early years. Annual age-adjusted rates of cancer incidence (from cancer registries) were available for the period 1975 to 1997, and age-adjusted mortality rates were available for the period 1950 and 2000. Means of height and 

1b Observational Analytical Studies. Analytical studies, which can be observational or experimental, evaluate the determinants or causes of disease. Because of the ethical constraints for conducting experimental studies (discussed below), most epidemiological studies are observational. The major drawback of observational studies is that the observed groups may differ in many other characteristics in addition to the one that is being studied thus the role of a specific exposure may be more difficult to establish than in experimental studies. There are three major types of observational studies (1) follow-up or cohort studies, (2) case-control studies, and (3) cross-sectional studies. 

The major advantage of cohort studies is that exposure is measured before disease occurs and thus provides strong evidence of causality, given that the exposure of interest will be unlikely to be affected by disease status. Other advantages of cohort studies are that they allow measurement of disease in the exposed and unexposed population, can measure multiple outcomes, can evaluate rare exposures, and are not subjected to some types of biases, such as recall bias (see Section 26.2.4 for a description of biases). Disadvantages include (a) the requirement of large number of subjects, (b) expense, (c) requirement of an extensive time to set up and follow up, (d) cannot be used to evaluate rare diseases, and (e) can be associated with some type of biases such as selection bias. 

Example 2. The Cancer Prevention Cohort Study (CPS II) mortality cohort consists of 1.2 million adults residing in 50 states, the District of Columbia, and Puerto Rico. Individuals in this cohort completed self-administered questionnaires in 1982 with information on race, diet, exercise, medical history, and other lifestyle factors. Findings on the relationship between colorectal cancer and meat consumption on a subset 

Case-Control Studies. These are retrospective studies that enroll individuals with disease (cases) and without disease (controls) at the beginning of the study. The prevalence of the exposure of interest is then compared between the controls and the cases. Cases may be incident, which are new cases that are identified in a defined time period, or prevalent, which are all the cases that have occurred up to a certain point in time. Controls can be selected from the population (such as the same geographical region as cases) or from the same hospitals as the cases hospital controls are individuals who have disease other than the disease of interest. When using hospital-based controls, care should be taken not to select individuals with diseases that may share the same risk factors as the disease under study. To make subjects as comparable as possible, with the exception of the disease of interest, controls are often matched (either individually or by frequency) to the cases for age, sex, ethnicity, and other relevant variables. 

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Kiso M, Mitamura K, Sakai-Tagawa Y, Shiraishi K, Kawakami C, Kimura K, Hayden FG, Sugaya N, Kawaoka Y (2004) Resistant influenza A viruses in children treated with oseltamivir descriptive study. Lancet 364 759-765... 

Quality of evidence I, evidence from >1 properly randomized, controlled trial II, evidence from <1 well-designed clinical trial, without randomization from cohort or case-controlled analytic studies (preferably from >1 center) or from multiple time-series III, evidence from opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees. 

III, Evidence from opinions of respected authorities based on clinical experience, descriptive studies, or reports of consulting committees. 

Steiner, A. L. (1973) Self- and allo-grooming behavior in some ground squirrels (Sciuridae), descriptive study. Can. J. Zool. 51, 151-161. 

A. Terminological-descriptive Value Chain Management Chemical Industry and Value Chain Characteristics Define the research field and basic terms Use of descriptive studies to narrow problem area investigated within research field Definition of types and relevant dimensions in the scope... 

Bayer A and Tadd W (2000) Unjustified exclusion of elderly people from studies submitted to research ethics committee for approval descriptive study. BMJ 321(7267) 992-993... 

Bugeja G, Kumar A, Banerjee AK (1997) Exclusion of elderly people from clinical research a descriptive study of published reports. BMJ 315(7115) 1059... 

Well-designed non-experimental descriptive studies for example comparative,... 

These types of data are too often over-interpreted, and taken to provide more insight than is possible. The well-trained epidemiologist understands the limits, knows that, at most, such data only suggest where to look for more telling information. Descriptive studies are exceedingly important clues to the causation problem, but are no more than that. 

Different methods are used in epidemiology. Epidemiological studies are often divided into descriptive studies and analytic studies. 

Descriptive studies may be defined as studies that describe the patterns of disease occurrence by time, place, and person (WHO 2002). 

Types of descriptive studies include case reports or case series, and ecological studies. 

Myton T Fletcher K (2003). Descriptive study of the effects of altering formulation of prescribed methadone from injectable to oral. Psychiatric Bulletin, 27, 3-6... 

Nevertheless, development of toxicology as a separate science has been slow, particularly in comparison with subjects such as pharmacology and biochemistry, and toxicology has a much more limited academic base. This may in part reflect the nature of the subject, which has evolved as a practical art, and also the fact that many practitioners were mainly interested in descriptive studies for screening purposes or to satisfy legislation. 

Several methods the epidemiologist has for investigating relationships vary greatly in cost, time and energy expended, and analytic and interpretive value. The descriptive study is simply, as the name implies, a series of rates, ratios, and proportions which help describe either the exposure or the outcome in detail. The case-control study is relatively easy to carry out, and new analytic techniques have already increased its interpretive value. An exposure study, although not strictly in the realm of epidemiology, documents exposure in various substrata of a population. 

The following three accounts of waste-site investigations demonstrate four major approaches to assessing health effects at hazardous waste sites (1) Descriptive studies, (2) case-control studies, (3) studies, and (4) cohort studies. 

Descriptive studies do not formally test hypotheses rather, they generate hypotheses based on evaluation of research questions. As such, descriptive designs cannot assess causality. One common descriptive design that offers considerable information on selected outcomes, such as birth defects, is the case series design. As the name suggests, this design encompasses a series of cases with the same outcome. There is no comparison group. This type of study can raise... 

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