Theo was doing research to support the claim that exercise increases heart and lung health. He had 50 people do a rigorous exercise program. Each week, for six months, he tested their heart and respiratory rate. He determined that exercise does increase heart and lung health.
Answer
A
It is valid because he used multiple trials.
B
It is invalid because he did not have a control group.
C
It is invalid because his sample size was small.
D
It is valid because he controlled the exercise program.