19 Key Terms Point estimate -- a single value that represents some unknown population characteristic, such as the population mean. Condence interval A range of values that, with a known degree of certainty, includes an unknown population characteristic, such as a population mean. Level of condence The percent of time that a series of condence intervals includes the unknown characteristic, such as the population mean. Ma_rgjn of error That which is added to and subtracted from some sample value, such as the sample proportion or sample mean, to obtain the limits of a condence interval. Text Review A researcher may wish to estimate the value of a population mean rather than test a hypothesis based on a population mean. Estimation is possible with use of (1) and (2) . A point estimate is a single value that represents some unknown (3) characteristic. The problem with point estimates is that they tend to be (4) because of (5) . Therefore, the researcher uses a more accurate type of estimate, (6) . A condence interval is a range of values that, with a known degree of certainty, includes an unknown population characteristic, such as (7) . To understand condence intervals, you must be aware of three important properties of the sampling distribution of the mean. (a) The mean of the sampling distribution always equals the (8) . (b) The standard error of the sampling distribution equals the population standard deviation divided by the square root of the (9) . (c) The shape of the sampling distribution approximates a normal distribution if sample size satises the