The November 17, 1994 issue of The New England Medical Journal reported on a study of the effects of hormone therapy on middle-aged women. About 750 women took part in the study; half were selected randomly to receive the hormone therapy and the other half were given a placebo (they did not know which). After about a year, blood tests were conducted on each subject by a lab technician who was unaware of which group (treatment or placebo) the blood samples originated from. In presenting the results of the experiment, the authors reported that the women in the treatment group had experienced a statistically significant increase in HDL (the so-called "good" cholesterol) and a statistically significant reduction in LDL (the so-called "bad" cholesterol) when compared with the control group. What type of design is this study?
1) This is an example of a block design.
2) This is an example of a completely randomized design.
3) This is an example of a matched pairs design.
4) This study would be classified as un-blinded.
5) This study would be classified as single-blinded.
6) This study would be classified as double-blind.