21.   The researchers also compared the incidence of violence among mentally ill persons in Pittsburgh with that of the general population in the neighborhoods where they lived.

22.   The researchers compared that sample with others to build a family tree to trace changes in the fast-mutating AIDS virus.

23.   The researchers compared the time of ice breakup with weather records from Nenana and Fairbanks and found that the time correlated well with temperature change over the decades.

24.   The researchers are comparing fluid drained from patients with severe head trauma to relieve a buildup of pressure with fluid from patients given spinal taps for other reasons.

25.   The researchers compared old and new X-ray measurements of the volume of blood pumped with each heartbeat.

26.   The researchers compared the effects of those beverages with the effects of decaffeinated coffee.

27.   The researchers compared the women who had epidurals with women who had other kinds of pain relief or who had no pain medicine at all.

28.   The researchers compared their results with earlier neutrino counts from the Super-Kamiokande neutrino experiment in Japan, which primarily detects collisions between electron neutrinos and electrons.

29.   The researchers compared women by body mass index, a number that combines weight and height.

30.   The researchers compared the incidence of reported back pain and back injury claims among workers who used the belts and those who did not.