A confidence interval can be constructed using formula 17.1, where a value of z from the standard normal table is multiplied by the standard error (S.E.) and this value is both added to and subtracted from the mean. In order to use this formula, the (11) ---------

must be known and sample size must be at least (12)---------

In practice, only one confidence interval is actually constructed, and it is either (13)______ or (14)_______. Although we never really know whether a particular confidence interval is true or false, we can be reasonably confident when the level of confidence is 95% or more. The level of confidence indicates the percent of time that a series of confidence intervals includes the unknown population characteristic such as the population mean. An increase in confidence interval causes a wider confidence interval that is less (15)________________________ unless it is offset by an increase in (16)_______________________________.