The study involved forty-four traders and their profits and losses over a twenty-month period ending in two thousand seven.

VOA: special.2009.02.25

The study examined employment records for eight cities in Minnesota for a three-year period through two thousand six.

VOA: special.2009.05.27

The researchers studied the diets of thirty-one thousand children ages two to eighteen over a thirty-year period.

VOA: special.2010.03.17

They had six children over a seven-year period, four girls and two boys.

VOA: special.2010.04.18