The gradual spread of the programme over the country gave us the possibility to use a control group, creating a quasi-experimental situation.
The first two were randomized controlled trials and the third used a control group.
The study used a control group, which was given only brief advice on the benefits of activity.
The researchers used a control group of women who were accessing support for domestic violence but whose partner was not attending a DVPP in order to compare results.
But Dr. Siegel and other researchers said those findings were not as persuasive because the state had not used a control group.
"We've done tests exposing women and young girls to adverts with these models in, using a control group exposed to different images.
The farmers will also conduct a number of randomized trials by using a control group of crops to compare the health of new seed varieties with the old varieties.
Wallerstein was widely faulted for her failure to use a control group: she interviewed mopey, disgruntled children from divorced homes but didn't compare them with children from intact families, many of whom are, of course, mopey and disgruntled, too.
At the outset, a researcher named Roland Fryer suggested that the city select schools via random assignment, using a control group for comparison.
