This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
When an intervention is applied to community to evaluate its usefulness, it is termed as a trial for - 
Select and explain. 
A. Efficacy, B. Effectiveness, C. Efficiency, D. Effect modification
B: Effectiveness
Answer: B: Effectiveness 
Explanation: EVALUATION OF HEALTH SERVICES:

Efficacy: Is the effect or usefulness of an agent/ drug/ vaccine under ideal ‘controlled laboratory’ conditions
Effectiveness: Is the effect or usefulness of an agent/ drug/ vaccine in real life community situations
Efficiency: Is the measure of relationship between the results achieved and the effort expended in terms of money, resources and time

– Efficiency: Output/ Input
– Evaluation of efficiency:
1. Cost-benefit analysis: Both input as well as output is in monetary terms
2. Cost-effectiveness analysis: Input is in monetary terms whereas output is in terms of ‘no. of lives saved'.