Common Mistakes : Effective

adjective

.BAD: British farmers receive only a little aid since their farms are relatively effective
.GOOD: British farmers receive only a little aid since their farms are relatively efficient

.BAD: Aspirin is very effective to relieve pain
.GOOD: Aspirin is very effective in relieving pain

: be effective in doing sth
Doctors soon realized that this drug was also effective in relieving the symptoms of arthritis