Measures To Consider When Evaluating Training ROI

People often ask questions, such as, "What kinds of metrics are most commonly used to measure ROI?" There then follows discussions on the kinds of measures used, or that shouldn't be used, and sometimes the conversation goes off track and conflict brakes out. While people may be happy with the concept of conducting an ROI of training, they may be less happy with how to do it, just what measures should be considered? Is there a standard set or is every organization or training intervention different and therefore needing its own set of measures?