Acceptance criterion - The maximum number of defective items that can be found in the sample and still allow acceptance of the lot.
Acceptance sampling - A statistical procedure in which the number of defective items found in a sample is used to determine whether a lot should be accepted or rejected.
Addition law - A probability law used to compute the probability of a union of two events, denoted A and B. It is P(AÈB)=P(A)+P(B)-P(AÇB). For mutually exclusive events, because P(AÇB)=0, it reduces to P(AÈB)=P(A)+P(B).
Adjusted multiple coefficient of determination - A measure of the goodness of fit of the estimated multiple regression equation that adjusts for the number of independent variables in the model and thus avoids overestimating the impact of adding more independent variables.
Aggregate price index - A composite price index based on the prices of a group of items.
Alternative hypothesis - The hypothesis concluded to be true if the null hypothesis is rejected.
ANOVA table - A table used to summarize the analysis of variance computations and results. It contains columns showing the source of variation, the sum of squares, the degrees of freedom, the mean square, and the F values.
Assignable causes - Variations in process outputs that are due to factors such as machine tools wearing out, incorrect machine settings, poor-quality raw materials, operator error, and so on. Corrective action should be taken when assignable causes of output variation are detected.
Autocorrelation - Correlation in the errors that arises when the error terms at successive points in time are related.
Autoregressive model - A time series model whereby a regression relationship based on past time series values is used to predict the future time series values.
B
Bar graph - A graphical device for depicting data that have been summarized in a frequency distribution, relative frequency distribution, or percent frequency distribution.
Basic requirements of probability - Two requirements that restrict the manner in which probability assignments can be made: (1) for each experimental outcome Ei we must have 0<P(Ei)<1; (2) considering all experimental outcomes, we must have P(E1)+ P(E2)+...+P(En)=1.
Bayes' theorem - A method used to compute posterior probabilities.
Binomial experiment - A probability experiment having the following four properties: consists of n identical trials, two outcomes (success and failure) are possible on each trial, probability of success does not change from trial to trail, and the trials are independent.
Binomial probability distribution - A probability distribution showing the probability of x successes in n trials of a binomial experiment.
Binomial probability function - The function used to compute probabilities in a binomial experiment.
Blocking - The process of using the same or similar experimental units for all treatments. The purpose of blocking is to remove a source of variation from the error term and hence provide a more powerful test for a difference in population or treatment means.
Bound on the sampling error - A number added to and subtracted from a point estimate to create an approximate 95% confidence interval. It is given by two times the standard error of the point estimator.
Box plot - A graphical summary of data. A box, drawn from the first to the third quartiles, shows the location of the middle 50% of the data. Dashed lines, called whiskers, extending from the ends of the box show the location of data values greater than the third quartile and data values less than the first quartile. The locations of any outliers are also noted.
C
Causal forecasting methods - Forecasting methods that relate a time series to other variables that are believed to explain or cause its behavior.
Central limit theorem - A theorem that enables one to use the normal probability distribution to approximate the sampling distribution of the sample mean and sample proportion whenever the sample size is large.
Chebyshev's theorem - A theorem applying to any data set that can be used to make statements about the proportion of items that must be within a specified number of standard deviations of the mean.
Class midpoint - The point in each class that is halfway between the lower and upper class limits.
Classical method - A method of assigning probabilities that assumes the experimental outcomes are equally likely.
Cluster sampling - A probability sampling method in which the population is first divided into clusters and then one or more clusters are selected for sampling. In single-stage cluster sampling, every element in each selected cluster is sampled; in two-stage cluster sampling, a sample of the elements in each selected cluster is collected.
Coefficient of determination - A measure of the goodness of fit of the estimated regression equation. It can be interpreted as the proportion of the variation in the dependent variable y that is explained by the estimated regression equation.
Coefficient of variation - A measure of relative variability for a data set, found by dividing the standard deviation by the mean and multiplying by 100.
Common causes - Normal or natural variations in process outputs that are due purely to chance. No corrective action is necessary when output variations are due to common causes.
Comparisonwise Type I error rate - The probability of a Type I error associated with a single pairwise comparison.
Complement of event A - The event consisting of all sample points that are not in A.
Completely randomized design - An experimental design in which the treatments are randomly assigned to the experimental units.
Conditional probability - The probability of an event given that another event has occurred. The conditional probability of A given B is P(A|B)=P(AÇB)/P(B).
Confidence Coefficient - The confidence level expressed as a decimal value. For example, .95 is the confidence coefficient for a 95% confidence level.
Confidence interval estimate - The interval estimate of the mean value of y for a given value of x.
Confidence level - The confidence associated with an interval estimate. For example, if an interval estimation procedure provides intervals such that 95% of the intervals formed using the procedure will include the population parameter, the interval estimate is said to be constructed at the 95% confidence level.
Consistency - A property of a point estimator that is present whenever larger sample sizes tend to provide point estimates closer to the population parameter.
Consumer Price Index - A price index that uses the price changes in a market basket of consumer goods and services to measure the changes in consumer prices over time.
Consumer's risk - The risk of accepting a poor-quality lot. This is the Type II error.
Contingency table A table used to summarize observed and expected frequencies for a test of independence.
Continuous random variable - A random variable that may assume any value in an interval or collection of intervals.
Control chart - A graphical tool used to help determine whether a process is in control or out of control.
Convenience sampling - A nonprobabilistic method of sampling whereby elements are selected on the basis of convenience.
Cook's D - A measure of the influence of an observation based on the residual and leverage.
Correlation coefficient - A numerical measure of the strength of the linear association between two variables that takes values between -1 and +1. Values near +1 indicate a strong positive linear relationship, values near -1 indicate a strong negative linear relationship, and values near zero indicate lack of a linear relationship.
Covariance - A numerical measure of linear association between two variables. Positive values indicate a positive relationship; negative values indicate a negative relationship.
Critical value - A value that is compared with the test statistic to determine whether H0 should be rejected.
Cross-sectional data - Data collected at the same or approximately the same point in time.
Crosstabulation A tabular summary of data for two variables. The classes for one variable are represented by the rows; the classes for the other variable are represented by the columns.
Cumulative frequency distribution - A tabular summary of quantitative data showing the number of items with values less than or equal to the upper class limit of each class.
Cumulative percent frequency distribution - A tabular summary of quantitative data showing the percentage of items with values less than or equal to the upper class limit of each class.
Cumulative relative frequency distribution - A tabular summary of quantitative data showing the fraction or proportion of items with values less than or equal to the upper class limit of each class.
Cyclical component - The component of the time series model that results in periodic above-trend and below-trend behavior of the time series lasting more than one year.
D
Data set - All the data collected in a particular study.
Data - The facts and figures that are collected, analyzed, and interpreted.
Degrees of freedom - A parameter of the t distribution. When the t distribution is used in the computation of an interval estimate of a population mean, the appropriate t distribution has n-1 degrees of freedom, where n is the size of the simple random sample.
Delphi method - A qualitative forecasting method that obtains forecasts through group consensus.
Dependent variable - The variable that is being predicted or explained. It is denoted by y.
Descriptive statistics - Tabular, graphical, and numerical methods used to summarize data.
Deseasonalized time series - A time series from which the effect of season has been removed by dividing each original time series observation by the corresponding seasonal index.
Discrete random variable - A random variable that may assume either a finite number of values or an infinite sequence of values.
Discrete uniform probability distribution - A probability distribution for which each possible value of the random variable has the same probability.
Distribution-free methods - Another name for nonparametric statistical methods that indicates the lack of assumptions about the population probability distribution.
Dot plot - A simple graphical summary of data with each observation represented by a dot placed above a horizontal axis that shows the range of values for the observations.
Dow Jones averages - Aggregate price indexes designed to show common stock price trends and movements on the New York Stock Exchange.
Dummy variable - A variable used to model the effect of qualitative independent variables. A dummy variable may take only the value zero or one.
Durbin-Watson test - A test to determine whether first-order autocorrelation is present.
E
Elements - The entities on which data are collected.
Empirical rule - A rule that states the percentages of items that are within one, two, and three standard deviations from the mean for mound-shaped, or bell-shaped, distributions.
Estimated multiple regression equation - The estimate of the multiple regression equation based on sample data and the least squares method.
Estimated regression equation - The estimate of the regression equation developed from sample data by using the least squares method. For simple linear regression, the estimated regression equation is y = b0+b1x.
Event - A collection of sample points.
Expected value - A measure of the mean, or central location, of a random variable.
Experiment - A process that generates well-defined outcomes.
Experimental units - The objects of interest in the experiment.
Experimentwise Type I error rate - The probability of making a Type I error on at least one of several pairwise comparisons.
Exploratory data analysis - Methods that use simple arithmetic and easy-to-draw graphs to summarize data quickly.
Exponential probability distribution - A continuous probability distribution that is useful in computing probabilities for the time it takes to complete a task.
Exponential smoothing - A forecasting technique that uses a weighted average of past time series values to arrive at smoothed time series values that can be used as forecasts.
F
Factor - Another word for the independent variable of interest.
Factorial experiment - An experimental design that allows statistical conclusions about two or more factors.
Finite population correction factor - The term that is used in the formulas for and whenever a finite population, rather than an infinite population, is being sampled. The generally accepted rule of thumb is to ignore the finite population correction factor whenever n/N < .05.
Five-number summary - An exploratory data analysis technique that uses the following five numbers to summarize the data set: smallest value, first quartile, median, third quartile, and largest value.
Forecast - A projection or prediction of future values of a time series.
Frame - A list of the sampling units for a study. The sample is drawn by selecting units from the frame.
Frequency distribution - A tabular summary of data showing the number (or frequency) of items in each of several non-overlapping classes.
G
General linear model - A model of the form y=b0+b1z1+b2z2+...+bpzp+e, where each of the independent variables zj, j=1, 2,..., p, is a function of x1, x2,..., xk, the variables for which data have been collected.
Goodness of fit test - A statistical test conducted to determine whether to reject a hypothesized probability distribution for a population.
Grouped data - Data available in class intervals as summarized by a frequency distribution. Individual values of the original data are not available.
Hinges - The value of the lower hinge is approximately the first quartile, or 25th percentile. The value of the upper hinge is approximately the third quartile, or 75th percentile. The values of the hinges and quartiles may differ slightly because of differing computational conventions.
Histogram - A graphical presentation of a frequency distribution, relative frequency distribution, or percent frequency distribution of quantitative data constructed by placing the class intervals on the horizontal axis and the frequencies on the vertical axis.
Hypergeometric probability function - The function used to compute the probability of x successes in n trials when the trials are dependent.
I
Independent events Two events A and B where P(A|B)=P(A) or P(B|A)=P(B); that is, the events have no influence on each other.
Independent samples - Samples selected from two (or more) populations in such a way that the elements making up one sample are chosen independently of the elements making up the other sample(s).
Independent variable - The variable that is doing the predicting or explaining. It is denoted by x.
Index of Industrial Production - A quantity index that is designed to measure changes in the physical volume or production levels of industrial goods over time.
Influential observation - An observation that has a strong influence or effect on the regression results.
Interaction - The effect produced when the levels of one factor interact with the levels of another factor in influencing the response variable.
Interquartile range (IQR) - A measure of variability, defined to be the difference between the third and first quartiles.
Intersection of A and B - The event containing all sample points that are in both A and B. The intersection is denoted AÇB.
Interval estimate - An estimate of a population parameter that provides an interval believed to contain the value of the parameter.
Interval scale - A scale of measurement for a variable that has the properties of ordinal data and the interval between observations is expressed in terms of a fixed unit of measure. Interval data are always numeric.
Irregular component - The component of the time series model that reflects the random variation of the time series values beyond what can be explained by the trend, cyclical, and seasonal components.
J
Joint probability - The probability of two events both occurring; that is, the probability of the intersection of two events.
Judgment sampling - A nonprobabilistic method of sampling whereby element selection is based on the judgment of the person doing the study.
Kruskal-Wallis test - A nonparametric test for identifying differences among three or more populations.
Laspeyres index - A weighted aggregate price index in which the weight for each item is its base-period quantity.
Least squares method - The method used to develop the estimated regression equation. It minimizes the sum of squared residuals (the deviations between the observed values of the dependent variable, yi, and the estimated values of the dependent variable, yi).
Level of significance - The maximum probability of a Type I error.
Leverage - A measure of how far the values of the independent variables are from their mean values.
Lot - A group of items such as incoming shipments of raw materials or purchased parts as well as finished goods from final assembly.
M
Mann-Whitney-Wilcoxon (MWW) test - A nonparametric statistical test for identifying differences between two populations based on the analysis of two independent samples.
Margin of error - The ± value added to and subtracted from a point estimate in order to develop a confidence interval.
Matched samples - Samples in which each data value of one sample is matched with a corresponding data value of the other sample.
Mean Square Error - The unbiased estimate of the variance of the error term. It is denoted by MSE or s2.
Mean squared error (MSE) - An approach to measuring the accuracy of a forecasting model. This measure is the average of the sum of the squared differences between the forecast values and the actual time series values.
Mean - A measure of central location for a data set. It is computed by summing all the data values and dividing by the number of items.
Median - A measure of central location. It is the value that splits the data into two equal groups, one with values greater than or equal to the median and one with values less than or equal to the median.
Mode - A measure of location, defined as the most frequently occurring data value.
Moving averages - A method of forecasting or smoothing a time series by averaging each successive group of data points.
Multicollinearity - The term used to describe the correlation among the independent variables.
Multinomial population - A population in which each element is assigned to one and only one of several categories. The multinomial probability distribution extends the binomial probability distribution from two to three or more categories.
Multiple coefficient of determination - A measure of the goodness of fit of the estimated multiple regression equation. It can be interpreted as the proportion of the variation in the dependent variable that is explained by the estimated regression equation.
Multiple comparison procedures - Statistical procedures used to conduct statistical comparisons between pairs of the population means or treatments.
Multiple regression analysis - Regression analysis involving two or more independent variables.
Multiple regression equation - The mathematical equation relating the expected value or mean value of the dependent variable to the values of the independent variables.
Multiple regression model - The mathematical equation that describes how the dependent variable y is related to the independent variables x1, x2,..., xp and an error term e.
Multiple sampling plan - A form of acceptance sampling in which more than one sample or stage is used. On the basis of the number of defective items found in a sample, a decision will be made to accept the lot, reject the lot, or continue sampling.
Multiplication law - A probability law used to compute the probability of an intersection of two events, denoted A and B. It is P(AÇB)=P(A)P(B|A) or P(AÇB)= P(B)P(A|B). For independent events it reduces to P(AÇB)=P(A)P(B).
Multiplicative time series model - A model whereby the separate components of the time series are multiplied together to identify the actual time series value. When the four components of trend, cyclical, seasonal, and irregular are assumed present, we obtain Yt = Tt×Ct×St×It. When the cyclical component is not modeled, we obtain Yt=Tt×St×It.
Mutually exclusive events Events that have no sample points in common; that is, AÇB is empty and P(AÇB)=0.
N
Nominal scale - A scale of measurement for a variable that uses a label or name to identify an attribute of an element. Nominal data may be nonnumeric or numeric.
Nonparametric methods - Statistical methods that require few, if any, assumptions about the population probability distributions and the level of measurement. These methods can be applied when nominal or ordinal data are available.
Nonprobabilistic sampling - Any method of sampling for which the probability of selecting a sample cannot be computed.
Nonsampling error - All types of errors other than sampling error, such as measurement error, interviewer error, and processing error.
Normal probability distribution - A continuous probability distribution. Its probability density function is bell shaped and determined by its mean m and standard deviation s.
Normal probability plot - A graph of normal scores plotted against values of the standardized residuals. This plot helps determine whether the assumption that the error term has a normal probability distribution appears to be valid.
np chart - A control chart used to monitor the output of a process in terms of the number of defective items.
Null hypothesis - The hypothesis tentatively assumed true in the hypothesis testing procedure.
Observation - The set of measurements obtained for a single element.
Ogive - A graph of a cumulative distribution.
One-tailed test - A hypothesis test in which rejection of the null hypothesis occurs for values of the test statistic in one tail of the sampling distribution.
Operating characteristic curve - A graph showing the probability of accepting the lot as a function of the percentage defective in the lot. This curve can be used to help determine whether a particular acceptance sampling plan meets both the producer's and the consumer's risk requirements.
Ordinal scale - A scale of measurement for a variable that has the properties of nominal data and can be used to rank or order the data. Ordinal data may be nonnumeric or numeric.
Outlier - A data point or observation that does not fit the pattern shown by the remaining data; an unusually small or unusually large data value.
P
p chart A control chart used when the output of a process is measured in terms of the proportion defective.
Paasche index - A weighted aggregate price index in which the weight for each item is its current-period quantity.
Parameter - A numerical characteristic of a population, such as a population mean, a population standard deviation, a population proportion, and so on.
Partitioning - The process of allocating the total sum of squares and degrees of freedom to the various components.
Percent frequency distribution - A tabular summary of data showing the percentage of items in each of several nonoverlapping classes.
Percentile - A value such that at least p percent of the items are less than or equal to this value and at least (100-p) percent of the items are greater than or equal to this value. The 50th percentile is the median.
Pie chart - A graphical device for presenting data summaries based on subdivision of a circle into sectors that correspond to the relative frequency for each class.
Point estimate - A single numerical value used as an estimate of a population parameter.
Point estimator - The sample statistic that provides the point estimate of the population parameter.
Poisson probability distribution - A probability distribution showing the probability of x occurrences of an event over a specified interval of time or space.
Poisson probability function - The function used to compute Poisson probabilities.
Pooled variance - An estimate of the variance of a population based on the combination of two (or more) sample results. The pooled variance estimate is appropriate whenever the variances of two (or more) populations are assumed equal.
Population parameter - A numerical value used as a summary measure for a population of data (e.g., the population mean, the population variance, and the population standard deviation).
Population - The set of all elements of interest in a particular study.
Posterior probabilities - Revised probabilities of events based on additional information.
Power curve - A graph of the probability of rejecting H0 for all possible values of the population parameter not satisfying the null hypothesis. The power curve provides the probability of correctly rejecting the null hypothesis.
Power - The probability of correctly rejecting H0 when it is false.
Precision statement - A probability statement about the sampling error.
Prediction interval estimate - The interval estimate of an individual value of y for a given value of x.
Price relative - A price index for a given item that is computed by dividing a current unit price by a base-period unit price and multiplying the result by 100.
Prior probabilities - Initial estimates of the probabilities of events.
Probabilistic sampling - Any method of sampling for which the probability of each possible sample can be computed.
Probability density function - A function used to compute probabilities for a continuous random variable. The area under the graph of a probability density function over an interval represents probability.
Probability distribution - A description of how the probabilities are distributed over the values the random variable can assume.
Probability function - A function, denoted by f(x), that provides the probability that x assumes a particular value for a discrete random variable.
Probability - A numerical measure of the likelihood that an event will occur.
Producer Price Index - A monthly price index designed to measure changes in prices of goods sold in primary markets (i.e., first purchase of a commodity in nonretail markets).
Producer's risk - The risk of rejecting a good-quality lot. This is the Type I error.
p-value - The probability, when the null hypothesis is true, of obtaining a sample result that is at least as unlikely as what is observed. It is often called the observed level of significance.
Q
Qualitative data - Data that are labels or names used to identify an attribute of each element. Qualitative data may be nonnumeric or numeric.
Qualitative independent variable - An independent variable with qualitative data.
Qualitative variable - A variable with qualitative data.
Quality control - A series of inspections and measurements that determine whether quality standards are being met.
Quantitative data - Data that indicate how much or how many of something. Quantitative data are always numeric.
Quantitative variable - A variable with quantitative data.
Quantity index - An index that is designed to measure changes in quantities over time.
Quartiles - The 25th, 50th, and 75th percentiles, referred to as the first quartile, the second quartile (median), and third quartile, respectively. The quartiles can be used to divide the data set into four parts, with each part containing approximately 25% of the data.
R
R chart - A control chart used when the output of a process is measured in terms of the range of a variable.
Random variable - A numerical description of the outcome of an experiment.
Randomized block design - An experimental design employing blocking.
Range - A measure of variability, defined to be the largest value minus the smallest value.
Ratio scale - A scale of measurement for a variable that has all the properties of interval data and the ratio of two values is meaningful. Ratio data are always numeric.
Regression equation - The equation that describes how the mean or expected value of the dependent variable is related to the independent variable.
Regression model - The equation describing how y is related to x and an error term.
Rejection region - The range of values that will lead to the rejection of a null hypothesis.
Relative efficiency - Given two unbiased point estimators of the same population parameter, the point estimator with the smaller standard deviation is more efficient.
Relative frequency distribution - A tabular summary of data showing the fraction or proportion (relative frequency)-of data items in each of several non-overlapping classes.
Relative frequency method - A method of assigning probabilities on the basis of experimentation or historical data.
Replication - The number of times each experimental condition is repeated in an experiment.
Residual analysis - The analysis of the residuals used to determine whether the assumptions made about the regression model appear to be valid. Residual analysis is also used to identify unusual and influential observations.
Residual plots - Graphical representations of the residuals that can be used to determine whether the assumptions made about the regression model appear to be valid.
Residual - The difference between the observed value of the dependent variable and the value predicted using the estimated regression equation.
S
Sample point - An element of the sample space. A sample point represents an experimental outcome.
Sample space - The set of all experimental outcomes.
Sample statistic - A numerical value used as a summary measure for a sample (e.g., the sample mean, the sample variance, and the sample standard deviation). The value of the sample statistic is used to estimate the value of the population parameter.
Sample - A subset of the population.
Sampled population - The population from which the sample is taken.
Sampling distribution - A probability distribution consisting of all possible values of a sample statistic.
Sampling error - The absolute value of the difference between an unbiased point estimator and the corresponding population parameter. It is the error that occurs because a sample, and not the entire population, is used to estimate a population parameter.
Sampling unit - The units selected for sampling. A sampling unit may include several elements.
Sampling with replacement - Once an element has been included in the sample, it is returned to the population. A previously selected element can be selected again and therefore may appear in the sample more than once.
Sampling without replacement - Once an element has been included in the sample, it is removed from the population and cannot be selected a second time.
Scatter diagram - A graph of bivariate data in which the independent variable is on the horizontal axis and the dependent variable is on the vertical axis.
Scatter diagram - A graphical presentation of the relationship between two quantitative variables. One variable is shown on the horizontal axis and the other variable is shown on the vertical axis.
Scenario writing - A qualitative forecasting method that consists of developing a conceptual scenario of the future based on a well-defined set of assumptions.
Seasonal component - The component of the time series model that shows a periodic pattern over one year or less.
Serial correlation - Same as autocorrelation.
Sign test - A nonparametric statistical test for identifying differences between two populations based on the analysis of nominal data.
Simple linear regression - Regression analysis involving one independent variable and one dependent variable in which the relationship between the variables is approximated by a straight line.
Simple random sampling - Finite population: a sample selected such that each possible sample of size n has the same probability of being selected. Infinite population: a sample selected such that each element comes from the same population and the elements are selected independently.
Single-factor experiment - An experiment involving only one factor with k populations or treatments.
Smoothing constant - A parameter of the exponential smoothing model that provides the weight given to the most recent time series value in the calculation of the forecast value.
Spearman rank-correlation coefficient - A correlation measure based on rank-ordered data for two variables.
Standard deviation - A measure of variability for a data set, found by taking the positive square root of the variance.
Standard deviation - The positive square root of the variance.
Standard Error of the Estimate - The square root of the mean square error, denoted by s. It is the estimate of s, the standard deviation of the error term e.
Standard error - The standard deviation of a point estimator.
Standard normal probability distribution - A normal distribution with a mean of zero and a standard deviation of one.
Standardized residual - The value obtained by dividing a residual by its standard deviation.
Statistical inference - The process of using data obtained from a sample to make estimates or test hypotheses about the characteristics of a population.
Statistics - The art and science of collecting, analyzing, presenting, and interpreting data.
Stem-and-leaf display - An exploratory data analysis technique that simultaneously rank orders quantitative data and provides insight about the shape of the distribution.
Stratified random sampling - A probability sampling method in which the population is first divided into strata and a simple random sample is then taken from each stratum.
Stratified simple random sampling - A probabilistic method of selecting a sample in which the population is first divided into strata and a simple random sample is then taken from each stratum.
Studentized deleted residuals - Standardized residuals that are based on a revised standard error of the estimate obtained by deleting observation i from the data set and then performing the regression analysis and computations.
Subjective method - A method of assigning probabilities on the basis of judgment.
Systematic sampling - A method of choosing a sample by randomly selecting the first element and then selecting every kth element thereafter.
Systematic sampling - A probability sampling method in which we randomly select one of the first k elements and then select every kth element thereafter.
T
t Distribution - A family of probability distributions that can be used to develop interval estimates of a population mean whenever the population standard deviation is unknown and the population has a normal or near-normal probability distribution.
Target population - The population about which inferences are made.
Test statistic - A statistic whose value is used to determine whether a null hypothesis can be rejected.
Time series data - Data collected at several successive periods of time.
Time series - A set of observations measured at successive points in time or over successive periods of time.
Treatment - Different levels of a factor.
Tree diagram - A graphical representation helpful in identifying the sample points of an experiment involving multiple steps.
Trend - The long-run shift or movement in the time series observable over several periods of time.
Two-tailed test - A hypothesis test in which rejection of the null hypothesis occurs for values of the test statistic in either tail of the sampling distribution.
Type I error - The error of rejecting H0 when it is true.
Type II error - The error of accepting H0 when it is false.
U
Unbiasedness - A property of a point estimator when the expected value of the point estimator is equal to the population parameter it estimates.
Uniform probability distribution - A continuous probability distribution for which the probability that the random variable will assume a value in any interval is the same for each interval of equal length.
Union of events A and B - The event containing all sample points that are in A, in B, or in both. The union is denoted AÈB.
Variable selection procedures - Methods for selecting a subset of the independent variables for a regression model.
Variable - A characteristic of interest for the elements.
Variance - A measure of variability for a data set, based on the squared deviations of the data values about the mean. It is also a measure of the variability, or dispersion, of a random variable.
Venn diagram - A graphical representation for showing symbolically the sample space and operations involving events in which the sample space is represented by a rectangle and events are represented as circles within the sample space.
W
Weighted aggregate price index - A composite price index in which the prices of the items in the composite are weighted by their relative importance.
Weighted mean - The mean for a data set obtained by assigning each data value a weight that reflects its importance within the set.
Weighted moving averages - A method of forecasting or smoothing a time series by computing a weighted average of past data values. The sum of the weights must equal one.
Wilcoxon signed-rank test - A nonparametric statistical test for identifying differences between two populations based on the analysis of two matched or paired samples.
A
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X
chart - A control chart used when the output of a process is measured in terms of the mean value of a variable such as a length, weight, temperature, and so on.