Why do some charts include straight line estimates and other charts include curved estimates?
In cases where we have very little poll data it is difficult for our standard estimator to filter out the noise in polling data due to random variation as well other methodological differences that make up a pollster’s “house effect.” For this reason, when we have very little data available (8 polls or fewer), we plot a straight line (linear regression) rather than our standard fitted curve (localized regression).
