Bias is a constant, systematic form or source of error, as opposed to variance, which is random, variable error. The nature and the extent of bias in survey [Page 57]measures is one of the most daunting problems that survey researchers face. How to quantify the presence of bias and how to reduce its occurrence are ever-present challenges in survey research. Bias can exist in myriad ways in survey statistics. In some cases its effect is so small as to render it ignorable. In other cases it is nonignorable and it can, and does, render survey statistics wholly invalid.