symmetric distribution

when the data values are evenly distributed about the mean

negatively or left-skewed distribution

when the majority of the data values fall to the right of the mean

positively or right-skewed

when the majority of the data values fall to the left of the mean

normal distribution

a continuous, symmetric, bell-shaped distribution of a variable

standard normal distribution

a normal distribution with a mean of 0 and a standard deviation of 1

sampling distribution of sample means

a distribution using the means computed from all possible random samples of a specific size taken from a population

sampling error

the difference between the sample measure and the corresponding population measure due to the fact that the sample is not a perfect representation of the population

standard error of the mean

standard deviation of the sample means

central limit theorem

as the sample size n increases without limit, the shape of the distribution of sample means taken with replacement from a population with mean "u" and standard deviation will approach a normal distribution.

correction for continuity

a correction employed when a continuous distribution is used to approximate a discrete distribution

z value (score)

the difference between a data value and the mean divided by the standard deviation

estimation

the process of estimating the value of a parameter from information obtained from a sample

robust

the distribution of the variable can depart somewhat from normality, and valid conclusions can still be obtained

point estimate

a specific numerical value estimate of a parameter

estimators

sample measures that are used to estimate population measures

unbiased estimator

the expected value or the mean of the estimates obtained from the samples of a given size are equal to the parameter being used

consistent estimator

as the sample size increases, the value of the estimator approaches the value of the parameter estimated

relatively efficient estimator

all of the statistics that can be used to estimate a parameter, & the estimator has a small variance

interval estimate

an interval or range of values used to estimate the parameter. the estimate may or may not contain the value of the parameter being estimated

confidence level

the probability that the interval estimate will contain the parameter, assuming that a large number of samples are selected and the estimation process on the same parameter is repeated.

confidence interval

a specific interval estimate of a parameter determined by using data obtained from a sample and by using the specific confidence level of the estimate

margin of error

the maximum likely difference between the point estimate of the parameter and the actual value of the parameter

degrees of freedom

the number values that are free to vary after a sample statistic has been computed, and they tell the researcher which specific curve to use when a distribution consists of a family of curves

proportion

a part of a whole, represented by a fraction, a decimal, or a percentage