A confidence interval (CI) is an interval estimate of a population parameter. It is a range of values, calculated from data, which is likely to include the true value of the parameter. When a newspaper reports “support for the government is 43 percent, in a poll with an error margin of 3 percent,” the 43 percent is a point estimate of the true level of support in the population. The CI is 43 ± 3 percent, or (40, 46 percent). The 3 percent is half the width of the CI, and is called the margin of error. The endpoints of the CI are the lower and upper limits or bounds.