<prompt> When an intervention is applied to community to evaluate its usefulness, it is termed as a trial for -EfficacyEffectivenessEfficiencyEffect modification  <response>: EVALUATION OF HEALTH SERVICES:Efficacy: Is the effect or usefulness of an agent drug vaccine under ideal controlled laboratory conditionsEffectiveness: Is the effect or usefulness of an agent drug vaccine in real life community situationsEfficiency: 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 terms2. Cost-effectiveness analysis: Input is in monetary terms whereas output is in terms of no. of lives saved. 