Manisha wanted to test the eating habits of her dog. She decided to study how the amount of food and the time of giving food affect the speed at which the dog ate. What is wrong with the design of Manisha's experiment and how can she correct it?

Question

Accepted Answer

The problem: Manisha is changing two independent variables at the same time — the amount of food AND the time of feeding. If the dog's eating speed changes, she cannot tell whether it was caused by the amount of food or by the feeding time, since both were varied together. This makes it impossible to draw a valid, reliable conclusion. Correction: She should test only ONE independent variable at a time while keeping the other constant. For example, first she should vary the amount of food while keeping the feeding time fixed (to see the effect of food amount), and in a separate set of trials, vary the feeding time while keeping the amount of food fixed (to see the effect of feeding time).