What is a 95 percent confidence interval? most common statistical standard What is a census? Researchers who enjoy complete access to their populations of interest are working with a census (as opposed to a sample). What is the central limit theorem? For random sampling with a large sample size n, the sampling distribution of the sample mean y is approximately a normal distribution. This holds no matter what the shape of the population distribution. The result also applies to proportions. What are degrees of freedom? the number of independent observations used to calculate a statistic

 What are inferential statistics? Provide predictions about a population, based on data from a sample of that population. What are the mean and standard error of y? Consider a random sample of size n from a population having mean μ and standard error σ. The sampling distribution of y gives the probabilities for the possible values of y. It has mean μ and standard error σy = σ/sqrt(n). What is the mean of a probability distribution? The expected value of a realization of the distribution, E(y). For a discrete variable, the mean, μ = ΣyP(y). What is the normal distribution? a distribution defined by a mathematical formula and the graph of which has a symmetrical, bell shape; in which the mean, mode, and median coincide; and in which a fixed proportion of observations lies between the mean and any distance from the mean measured in terms of the standard deviation

 What is the normal distribution? A symmetric, bell shaped distribution characterized by its mean, μ, and standard deviation, σ. The probability within any particular number of standard deviations of μ is the same for all normal distributions. This probability equals 0.68 within 1 standard deviation, .095 within 2 standard deviations, and 0.997 within 3 standard deviations. What is a population? all the cases or observations covered by a hypothesis; all the units of analysis to which a hypothesis applies What is a population parameter? the incidence of a characteristic or an attribute in a population (not a sample) What is probability? With a random sample or randomized experiment, the probability an observation has a particular outcome is the proportion of times that outcome would occur in a very long sequence of observations.

 What is a random sample? A set of observations randomly drawn from the population of interest. Random selection ensures the sample is representative of the population of interest. What is random sampling error? extent to which a sample statistic differs BY CHANCE from a population parameter What is random selection? Random selection occurs when every member of the population has an equal chance of being included in the sample. Define range. the distance between the highest and lowest values or the range of categories into which observations fall

 What is response bias? Response bias occurs when the subject gives an incorrect response (perhaps lying), or the question wording or the way the researcher asks a question is confusing or misleading. What is a sample? a subset of observations or cases drawn from a specified population What is a sample proportion? the number of cases falling into one category of the variable divided by the number of cases in the sample What is a sample statistic? the estimator of a population characteristic or attribute that is calculated from sample data

 What is a sampling distribution? The probability distribution that specifies probabilities for the possible values the statistic can take. What is a sampling frame? The population from which a sample is drawn. Ideally it is the same as the total population of interest to a study. What is selection bias? Selection bias occurs when non-random processes - often unknown to the researcher - cause differences between test (treatment) group and the control group. What is a standard deviation? A measure of dispersion of data points about the mean for interval- and ratio-level data. Standard deviation is equal to the square root of variance, and describes a typical distance from the mean.

 What is a standard error? The standard deviation of the sample distribution of y is called the standard error of y. The standard error of y is denoted by σy. What is a standard error? The standard deviation of the sample distribution of y is called the standard error of y. The standard error of y is denoted by σy. What is the standard normal distribution? The normal distribution with mean μ = 0 and standard deviation σ = 1. What is standardization? occurs when the numbers in a distribution are transformed into standard units of deviation from the mean of the distribution

 What is the Student's t-distribution? a probability distribution that can be used to make inferences about a population mean when the sample size is small What is variance? A measure of dispersion of data points about the mean for interval- and ratio-level data. Variance averages the squared deviations about the mean. What is a Z score? the number of standard deviations by which a score deviates from the mean score What is cumulative density (of a distribution)? Equals the proportion (or percentage) of the area under the curve less than a given Z score.

 What is the empirical rule? What a normal distribution follows, where researchers can know example how often a normally distributed variable falls within one, two, and three standard errors of its mean: 68, 95, and 99% respectively.