An impact evaluation is a study that measures the actual outcomes and consequences of a change. It takes into account both intended and unintended effects of the change, and aims to determine its overall impact. This means that a program or project may achieve its goals, but have negative unintended consequences. On the other hand, a program that is perceived as a failure due to budget and schedule issues may actually have a more positive impact than originally anticipated by its planners. Impact evaluations help organizations understand the full range of impacts of a change and can inform decision-making about future changes or interventions. The following are illustrative examples of an impact evaluation.

Cities

A city expands its highway system to more lanes only to discover that within a few short years traffic jams have once again become a common occurrence. An impact study indicates that the new lanes encouraged development of land further from the downtown core making the city less dense and increasing average commuting distance.

Transportation

A program to develop a system of high speed trains is initially viewed as a failure as it exceeds planned budget. However, within a decade ridership is far greater than business plans had anticipated. The overall impact on the economy, quality of life and the environment can be demonstrated to be exceedingly positive.

Education

An education system abandons standardized testing in high schools in favor of tests crafted by individual teachers. A later impact study looked at data before and after to determine that grade inflation occurred with the abandonment of the standard tests. This led universities and colleges to begin to rank schools and apply more complex admission processes than were far less transparent to students.

Marketing

A newspaper begins aggressively optimizing the titles of its articles with A/B testing. This immediately increases overall revenue. A later impact study indicates that the quality of titles dropped dramatically such that titles often didn’t reflect the content of articles. The optimization effort was associated with a steady decline in reputation, customer satisfaction and subscription rates.