These scenarios produce a chain reaction where individuals react to the policy changes first and then, depending on the design of the model, may also react to the reaction of other individuals. The results are the potential future outcome of the reform and are often compared with the base case to evaluate the potential impact of the reform. Microsimulation models require large amounts of data to effectively assemble a sample that adequately represents the whole population of interest and includes all of the characteristics of interest. Data are often gathered from a variety of sources, and sophisticated statistical techniques are often required to standardize the various databases so that they can be used to populate all of the desired attributes of individuals included in the sample.