Population living in metropolitan areas ( pctmetro), the percent of the population People ( crime), murders per 1,000,000 ( murder), the percent of the Variables are state id ( sid), state name ( state), violent crimes per 100,000 Sciences, Third Edition by Alan Agresti and Barbara Finlay (Prentice Hall, 1997). This dataset appears in Statistical Methods for Social How can we identify these three types of observations? Let’s look at an example datasetĬalled crime. Substantially changes the estimate of coefficients. Influence: An observation is said to be influential if removing the observation These leverage points can have an effect on the estimate of Leverage is a measure of how far an observation Leverage: An observation with an extreme value on a predictor variable is calledĪ point with high leverage. Or may indicate a data entry error or other problem. An outlier may indicate a sample peculiarity Given its values on the predictor variables. In other words, it is an observation whose dependent-variable value is unusual Outliers: In linear regression, an outlier is an observation with large Want to know about this and investigate further. Observation (or small group of observations) substantially changes your results, you would Make a large difference in the results of your regression analysis. Regression assumptions and detect potential problems using Stata.Ī single observation that is substantially different from all other observations can We will explore these methods and show how to verify Of Durham) has produced a collection of convenience commands which can beĭownloaded from SSC ( ssc install commandname). That can be downloaded over the internet. Stata has many of these methods built-in, and others are available Many graphical methods and numerical tests have been developed over the years for Related, can cause problems in estimating the regression coefficients.
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