Kinds of Studies....

Study Types: This meta-analysis combined several kinds of studies....35 clinical trials, 2 prospective studies, and 13 cross-sectional studies.
The clinical trials included ranged in sample size (number of people in the study) from the smallest (8 participants) to much larger (11,000+). They were conducted in multiple countries (Spain, Israel, Italy, U.S., U.K., Denmark, Australia, Sweden, Finland, Germany, France). The studies lasted differing periods of time, from 4 weeks, to 5 years.
Clinical trials are used in evaluating whether a drug, diet, or other type of treatment is effective. The best clinical trials include “randomization” (called a randomized clinical trial, or RCT), with people picked randomly from the population being studied. Even further randomization can be used to choose the participants that get the treatment/drug being studied, and the ones that are getting the old treatment, or no treatment (called controls). Then, the end result being measured (weight loss, decreased blood fats, etc.) is evaluated in all of the participants. To avoid any other bias or effect on the study results, it is helpful if neither the researchers or the participants know who got the new drug/treatment, and who got the old drug/treatment...this is called a double-blind study. Randomized clinical trials are considered to be some of the most reliable studies in measuring effectiveness (Gordis, 2009, p. 132).
Cross-sectional studies are used to get a “snap-shot” of a current situation, in trying to find out if there is a possible connection between an “exposure” and a “disease”. Both the exposure and disease are surveyed at the same time. So, in this particular situation, both diet and health indicators would be surveyed at the same time. This assessment of some health condition, or disease, in an identified population is the “prevalence” (how many people in a specific population have a specific condition). Limits of a cross-sectional study are that it can’t be used to measure look backward (measuring how long this disease has existed in the population, or duration), or which came first, the exposure or the disease (temporality)...So, these studies can be used to link or associate, but not to determine cause and effect....(Which came first, the chicken or the egg???....we know that they are associated, but don’t know what came first).