Econometric theory uses statistical theory and mathematical statistics to evaluate and develop econometric methods. Econometric models are statistical models used in econometrics. EViews is a statistical package for Windows, used mainly for time-series oriented econometric analysis. RATS is a powerful program, which can perform a range of econometric and statistical operations. These are more complex econometric and general equilibrium models. Structural change tests are a type of econometric hypothesis test. Econometric studies have identified the fiscal stimulus as especially effective. Generally, when testing for heteroskedasticity in econometric models, the best test is the White test. Bootstrapping can also be a supplement for econometric models. In econometric models, the parameters may be bimodally distributed. Eviews allows the user to assess econometric results easily. An overview of econometric methods used to study this problem were provided by Card (1999). The econometric goal is to estimate formula 46. These tend to be estimated from econometric studies, with 95% confidence intervals. He developed a body of new econometric tools that address these issues.