Effectiveness is a measure of the ability of the product or service to meet customer expectations. In other words, it is a measure of quality - how well the job gets done.
Defects received by customers, on-time shipments, customer satisfaction, customer loyalty and repeat business are all measures of effectiveness.
The advantage of Effectiveness metrics is that they speak to the customer's experience, unlike Efficiency metrics. If effectiveness measurements turn south, improved efficiency will have little long term value because the top line - sales revenue - will be negatively impacted.