Trivedi, Doll, and Khaw (2003) conducted an experiment to examine whether vitamin D supplementation improved bone health in men and women over 65. A total of 2,686 people aged 65-85 years living in the general community were randomly assigned to receive either oral vitamin D3 supplementation or a matching placebo (a look-alike pill with no pharmacological effect) every four months over five years. Those in the vitamin D group were less likely to have bone fractures than those in the placebo group. [Source:Trivedi, D. P., Doll, R., & Khaw, K. T. (2003). Effect of four monthly oral vitamin D3 (cholecalciferol) supplementation on fractures and mortality in men and women living in the community: randomised double blind controlled trial.British Medical Journal,326(7387), 469-475.]

In this experiment, thedependent variableis , and theindependent variableis .

The individuals who are in the control condition are typically referred to as the control group. Here, the control group consists of .

is a construct that is being tested in this experiment, and the experimenters have operationally defined it as .