Every year, millions of people start new diets. There is a bewildering array of diets to choose from. The question for many people is, which ones work?

Researchers at Tufts University in Boston made an attempt to point dieters in the right direction. Four diets were used:

1. Atkins low-carbohydrate diet

2. Zone high-protein, moderate carbohydrate diet

3. Weight Watchers diet

4. Dr. Ornish’s low-fat diet

The study recruited 160 overweight people and randomly assigned 40 to each diet. The average weight before dieting was 220 pounds and all needed to lose between 30 and 80 pounds. All volunteers agreed to follow their diets for 2 months. No exercise or regular meetings were required. The following variables were recorded for each dieter using the format shown here:

Column 1: identification number

Column 2: Diet

Column 3: Percent weight loss

Column 4: Percent low-density

lipoprotein (LDL)—”bad” cholesterol—decrease

Column 5: Percent high-density lipoprotein (HDL)—”good” cholesterol—increase

Column 6: quit after 2 months?

1 = yes, 2 = no

Column 7: quit after 1 year?

1 = yes, 2 = no

Is there enough evidence to conclude that there are differences between the diets with respect to

Percent weight loss?

Percent LDL decrease?

Percent HDL increase?

Proportion quitting within 2 months?

Proportion quitting after 1 year?