Jackson, LaCroix et. al (2006) present a quasi-experimental study examining the efficacy of supplementing calcium and vitamin D for prevention of bone fractures in postmenopausal women from ages 50 to 79. The design of this study develops a subjective population, contains factors to eliminate threats to validity, and reveals positives and negatives of studying a large population of subjects. The researchers state calcium along vitamin D intake can result in increased hip bone density, increase risk of kidney stones, and no reduced risk for bone fracture.
This study involves experimental protocol that studies 36,282 postmenopausal women from ages 50-79 who were presently participating in a Women’s Health Initiative clinical trial. The study becomes subjective to a target population of similar characteristics, because of a small variety in test subjects. The study contains a large number of test subjects which helps to validate the results. If one subject presents an error in the data, the large number of participants balances out the threat. Also, the study consists of participants from 40 different clinics across the country and this helps to eliminate any threats due to ecological or regional differences. Another control method to help reject these threats is the variety in demographic factors, health behavior, and medical history. The researchers used a double blind design to randomly assign women into a treatment or placebo group which rejects threats to internal validity of the study. With studying a population of this size, several concerns become apparent with control of the study. The researchers only examined the subjects when they were present at the clinical site. This presents a concern of external factors with the patients. The researchers could not control any additional supplements the subjects could have taken during the study that may