BOLD Educational Software Research and Statistics Glossary

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A	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Abbreviated Title	An identification of each manuscript page using the first two or three words from the title in the upper right-hand corner above or five spaces to the left of the page number.
Abstract	A brief but comprehensive summary of the contents of the document.
Action Research	A research method designed to develop new skills or new approaches to solving problems in the classroom or work setting.
Adjusted R squared	Because the R squared is estimated from a sample, it tends to over-estimate how well the models fits the population. Adjusted R squared is mathematically corrected to attempt to more closely reflect the goodness of fit of the model in the population.
Alpha coefficient	The estimated reliability of a measure.
Alpha level	The p-value for rejecting the null hypothesis, the probability of rejecting the null hypothesis when it is true (the probability of committing a type 1 error).
Alphanumeric variable	A variable that is entered in letters, or a combination of both letters and numbers.
Alternative hypothesis	A statistical hypothesis indicating that the value of the population parameter specified in the null hypothesis is incorrect.
Analysis of covariance	(ANCOVA) a type of analysis of variance procedure that attempts to control for scores on a pretest or other measure by using the combined application of linear regression and analysis of variance techniques.
Analysis of variance	(ANOVA) the parametric statistical procedure for determining the statistical significance of differences among two or more means.
Anecdotal evidence	Evidence that has been derived from stories or examples; evidence not based on empirical testing.
Anonymity	The assurance that no one, including the researcher, can link specific data to a specific participant/subject in the study
A posteriori probability	A probability assigned to an event that takes into account specific sample data already collected and analyzed.
Attribute	A specific value of a variable (e.g., red versus blue).
B	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Bell curve	A histogram depicts a normal distribution where most values cluster around a mean, while outliers can be found above and below the mean.
Bias	Error introduced into a research study through any means, such as a researcher's belief that a specific outcome is expected, participants behaving differently than they would were they not being observed, or any data collection or analysis procedure that does not accurately represent the population.
Biased estimator	A statistic whose expected value is not equal to the population value.
Bimodal distribution	A frequency distribution that has two modes.
Binary variable	A discrete random variable that has only two possible values, such as the flip of a coin (heads or tails). Such events are often described as success vs. failure.
Biserial correlation coefficient	The correlation between two variables, one measured on an interval scale and the other an artificial dichotomy with fundamental continuity.
Bivariate distribution	A distribution of scores of units or individuals on two variables.
Bivariate statistics	Analyses of two dependent variables (e.g., Pearson product-moment correlation coefficient).
Boxplot	A graphic that summarizes the distribution of an ordinal, interval, or ratio variable, indicating the median and quartiles as a box and extreme values as whiskers extending from the box.
C	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Case and Field research	A research method designed to study the background, status, and environmental interactions of a social unit (e.g., an individual, institution, or community).  Case and field research uses a qualitative methodology.
Case study	A qualitative study designed to examine a specific individual unit (e.g., a person, a class, an organization).
Categorical variable	A variable for which different scores represent differences in quality, not amount (e.g., male/female; red/blue).
Causal -comparative research	A research method design to investigate possible cause-and-effect relationships by observing existing variables and using statistical techniques such as correlation, regression, and path analysis to examine the data for likely causal factors. Causal-comparative research is similar to a quasi-experimental design, but with more compromises to the design, approaching a non-experimental design.
Causal relationship	A cause-effect relationship, normally demonstrated through experimental design.
Cell	A category in a table representing an intersection of levels of two or more variables.
Cell frequency	The number of cases having a specific combination of values.
Cell mean	The mean value of a dependent variable for all cases in a particular cell of an analysis of variance design.
Central tendency	A measure of a typical or average score in a distribution, usually the mean, median, or mode.
Chi-square	A statistic used to test the hypothesis that the row and column variables are independent.
Cluster sampling	The random selection of clusters (groups of population members) rather than individual population members.
Coding	The process or categorizing qualitative data, e.g., by theme.
Coefficient of alienation	The proportion of variation in Y that is not associated with differences in X.
Coefficient of determination	The proportion of variance that two variables have in common, computed by squaring the correlation coefficient.
Comparisonwise error rate	The probability of making a type 1 error for each comparison.
Concept mapping	A qualitative research process of creating a two-dimensional graph of a group's ideas, locating similar ideas closer together and dissimilar ideas further apart.
Conceptual framework	A written portion of a study, dissertation, or thesis that explains the key variables to be studied and the hypothesized relationships among them. The conceptual framework can be graphical or narrative, simple or elaborate.
Conclusions	The researcher’s interpretation of the data and analyses.
Concurrent validity	Statistical evidence used to defend the use of an instrument to predict other outcomes. Concurrent validity is demonstrated when an instrument correlates well with another instrument that has already been demonstrated to be a valid measure of the construct.
Confidence interval	An interval or range of scores within which there is a certain confidence that the population parameter will lay; the confidence interval is symmetric around the predicted true scores, not around the observed scores.
Confounding variables	Characteristics that, when undetected, can lead researchers to erroneous conclusions.
Constant	A characteristic or value that does not change.
Construct	A trait or attribute (e.g., motivation, attitude); theoretical constructions or abstractions aimed at organizing and making sense of our environment.
Construct validity	A measure of validity concerned with the validity of inferences about unobserved variables (constructs) on the basis of observed variables (their presumed indicators).
Content validity	A measure of validity that refers to some domain of content (e.g., social studies, vocabulary, job performance).
Continuous variable	A variable that can assume an infinite number of values.
Control group	The group in an experiment that is randomly assigned to receive the ordinary or traditional treatment (or none).
Convergent validity	The degree to which an instrument is similar to (or converges on) another instrument.
Correlated-samples t-test	A statistical procedure used to compare the means of two variables when scores on the variables are paired; also called a dependent-samples t-test and a paired-samples t-test.
Correlation	The linear association between two random variables X and Y.
Correlation coefficient	A measure of the linear relationship between two quantitative variables, also known as the Pearson r (Pearson Product Moment Correlation Coefficient), measured between -1 and 1.
Correlation matrix	A table that lists relationships of all variables in relation to each other.
Correlational research	A research method designed to investigate the extent to which changes in one variable relate to changes in one or more other variables using correlation coefficients.
Criterion	The probability that provides the basis for deciding whether a sample is too unlikely to have occurred by chance and thus is unrepresentative of a particular population.
Criterion validity	The extent to which the scores obtained from a procedure correlate with an observable behavior.
Criterion variable	See dependent variable.
Cronbach’s alpha	The average of all possible split-half reliabilities for a set of items. Split half reliability is the reliability between two parts of a test or instrument where those two parts are halves of the total instrument.
Cross tabulation	A table with a cell for every combination of values of two or more variables. The table shows the number of cases having each specific combination of values.
Curvilinear regression analysis	Regression analysis which assumes that the effect of the independent variable, X, on the dependent variable, Y, is not constant, as in linear regression, but that it varies for different values of X.
D	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Data	Observations or scores recorded.
Data analysis	The process within a research study following the formulation of the research questions and hypotheses and data gathering, when statistical analysis is performed. No formal evaluation is done during the analysis stage.
Data collection	The process within a research study following the formulation of the research questions and hypotheses when data is collected from subjects or elements within the sample.
Degrees of freedom	The number of scores in a sample that are free to vary; the number of observations minus the number of constraints on those observations.
Delimitations	The boundaries of the study purposely set by the researcher to narrow the scope.
Demographic variables	Variables used to describe the sample (e.g., gender, age, educational level).
Dependent variable	A variable that the researcher is attempting to explain in terms of one or more independent variables.
Descriptive research	A research method designed to systematically and accurately describe a situation or area of interest. Ethnographic research is one form of descriptive research that examines social behaviors within natural settings.
Descriptive statistics	The use of statistics to summarize and describe a group of scores or a set of data.
Developmental research	A research method designed to investigate changes in an individual or group over time.
Dichotomous variable	A variable that can have only two levels.
Directional hypothesis	A hypothesis that specifies the direction of a difference in means or of a relationship between variables.
Discrete random variable	A variable that can take on only a limited number of values (for example: whole numbers only).
E	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Effect size	An estimation of the magnitude of the relationship between two variables in a population based on a sample.
Empirical	Based on data or observations.
Ethnographic research	A form of descriptive research that examines social behaviors within natural settings.
Evaluation research	A research method designed to determine the relative merits of various products and approaches used in education.
Exempt research	Certain low-risk research is exempt from the requirements of the Federal regulations even though human subjects are involved.
Exhaustive	Each person, object, or item must be classified in one (and only one) category.
Expected value	The mean of the scores of a sampling distribution; a theoretical average value of a statistic over an infinite number of samples from the same population.
Experiment	A study in which at least one variable is manipulated and units are randomly assigned to the different levels or categories of the manipulated variable(s) and can therefore lead to statements regarding cause and effect.
Experimental research	A research method designed to examine possible cause-and-effect relationships by exposing one or more experimental groups to one or more treatment conditions and comparing the results to one or more control groups not receiving the treatment (random assignment being essential).
Experimentally accessible population	The available group of subjects from which the researcher obtains the sample.
Experimentwise error rate	The probability of incorrectly rejecting at least one true null hypothesis in an entire research study; in other words, the probability of making one or more type 1 errors in a series of analyses of dependent variables.
External validity	The ability to correctly generalize the results of a research study to other settings and subjects.
Extraneous variable	A variable not of interest to the researcher that might affect the results of a study.
Exploratory study	A research study designed to explore the relationships among key variables and formulate theories rather than to support a priori hypotheses.
F	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
F distribution	A frequency distribution of F ratios obtained from all possible samples of the same size. The F distribution is used in the calculations of analysis of variance and regression procedures.
Factor	A single discrete classification system for data, such that each item classified belongs to exactly one class (level) for that classification system.
Factor analysis	A statistical technique used to identify a relatively small number of factors that can be used to represent relationships among sets of many interrelated variables.
Factorial analysis of variance	Used when there are two or more categorical independent variables or factors in the research design; each main effect, as well as each interaction, is listed as a source in the analysis of variance summary table.
Factorial design	A research design that contains more than one independent variable.
F-test	A statistical procedure that involves computing the ratio of two sample variances, testing the null hypothesis that the population variances do not differ.
Frequency distribution	A list of all the scores for a sample or population indicating the number of times that each score occurs; the data are grouped into mutually exclusive categories showing the number of observations in each category.
Frequency polygon	Similar to a histogram, except line segments are used instead of bars – the points formed by the intersections of the class midpoints and the class frequencies.
G-I	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Gaussian distribution	Also called a normal distribution, data will follow a bell-shaped distribution.
Generalizability	The ability to apply the findings of a particular research study with a unique sample to a larger population. Generalizability is an issue of the external validity of the study.
Hermeneutics	The art or science of the interpretation of literature.
Histogram	A pictoral display of how many times any given score appears in the data set where the classes are marked on the horizontal axis and the class frequencies on the vertical axis. The class frequencies are represented by the heights of the bars, and the bars are drawn adjacent to each other.
Historical research	A research method designed to impartially examine and reconstruct the past.
Homogeneity of variance	Equal variances for the population from which the samples come.
Homoscedasticity	An equal spread of Y scores around the regression line.
Human Subject	A living individual included in research by an investigator who obtains data through intervention or interaction with the individual, or identifiable private information.
Hypothesis	The researcher's prediction, derived from a theory or speculation, about how two or more measured variables will be related to each other.
Implications	A statement by the researcher that logically connects the findings of the study to a set of recommended subsequent actions.
Independent samples t-test	A parametric statistical test used to compare the means of two groups in which the scores in one group are not paired with scores in the other group.
Independent variable	A variable that is manipulated in an experiment; the independent variable may be conceived of as cause to variables conceived of as effects (dependent variables) in the context of construct validation.
Inferential statistics	The use of statistics to test hypotheses and draw conclusions about a population based on data collected from a sample.
Informed consent	The voluntary choice of a human subject to participate in research based on an accurate understanding of its purposes, procedures, risks, benefits, alternatives, and any other factors that may affect a person's decision to participate. Informed consent consists of three steps: full disclosure of the nature of the research and the subject's participation, adequate comprehension on the part of the potential subjects, and the subject's voluntary choice to participate.
Institutional assurance	Documentation by an institution of its commitment to comply with Federal regulations, including the maintenance of adequate programs and procedures for the protection of human subjects.
Institutional Review Board	(IRB) A committee established by the institution to protect the rights and welfare of human subjects who participate in research conducted within the institution or under the auspices of the institution.
Instrumentation	The mechanism, equipment, survey, or test used to gather data.
Internal consistency reliability	A statistical method of testing the reliability of an instrument based on a single administration of the instrument.
Interval	A level of measurement where numbers represent the distance between the values of a characteristic; numbers may be meaningfully interpreted with respect to the attribute being measured (constant units of measurements are used). Data categories are mutually exclusive and exhaustive, are scaled according to the amount of the characteristic they possess, and equal differences in the characteristic are represented by equal differences in the numbers assigned to the categories.
Intervention	An action that will change, alter, or counter a present trend or circumstance; in an experiment, an intervention is a manipulation of the subject or the subject’s environment that is performed for research purposes.
L-M	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Least squares criterion	a mathematical procedure for finding the best fitting line to a given set of points by minimizing the sum of the squares of the offsets ("the residuals") of the points from the line. Each of the ‘POINTS’ is a representation of each individual based on their scores for both the given DEPENDENT VARIABLE (Y) and the INDEPENDENT VARIABLE (X).
Linear	The points depicting scores of individuals on both variables follow a trend that can be characterized by a straight line.
Mean	The arithmetic average computed by the sum of the scores divided by the total number of scores.
Mean square	In ANOVA, a MS is an estimated population variance. The Mean Square Within Groups (ANOVA) is the variability that occurs within the conditions or groups (variance NOT EXPLAINED), while the Mean Square Between Groups is the variability that occurs between conditions or groups (amount of variance explained). In Regression, the MS Within is referred to as the MS Regression, and the MS Between is referred to as the MS Residual.
Median	The score in the middle when the scores are arranged in order from the smallest to the largest (the 50th percentile).
Methodology	A description of the process by which data are gathered and analyzed during a study.
Mode	The score in a frequency distribution that occurs most often.
Multicollinearity	The existence of any correlations among the independent variables.
Multimodal	A distribution that has more than one mode.
Multiple correlation	A correlation coefficient between one variable and a linear combination of predictor variables, symbolized by R.
Multiple regression	A statistical procedure that creates an equation predicting a score on one variable from a linear combination of predictor variables.
Multiple standard error of estimate	A measure of the effectiveness of the regression equation in multiple regression analysis. It is measured in the same units as the dependent variable, and describes the amount of variation around the regression line.
Multivariate analysis of variance	(MANOVA) an extension of the analysis of variance procedure to deal with two or more dependent measures simultaneously; can be used to test complex dependencies of multiple dependent variables on categorical IVs.
Multivariate statistical techniques	A group of statistical techniques used for analyzing more than one dependent measure and/or more than one IV at a time.
Mutually exclusive	An individual or item that, by virtue of being included in one category, must be excluded from any other category.
N-O	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Nominal	A level of measurement where numbers represent different categories which are mutually exclusive and exhaustive; categories have no logical order.
Nonexperimental design	Research where both the independent variable and dependent variable are measured, not manipulated; can be used for prediction or association, but not to determine causal relationships.
Nonlinear regression	A parametric statistical procedure used to describe the relationship between the dependent variable and one or more independent variables in nonlinear fashion.
Nonparametric statistical tests	Statistical tests that do not make many assumptions about the nature of the population from which the sample comes, and that can be used with nominal and ordinal level data.
Nonresponse error	The statistical difference between a survey that includes only those who responded and a survey that also includes those who failed to respond.
Normal distribution	A theoretical frequency distribution that is bell shaped and symmetrical and in which the mean, median, and mode coincide; also called the normal curve or Gaussian distribution. The normal distribution is determined by its mean and variance.
Null hypothesis	A statement that there are no differences between two or more populations and any relationships (or differences) are due to chance.
Omnibus test	A test of significance that looks at all variables and/or all levels at the same time. An omnibus test is usually followed up with post hoc testing.
One-tailed test	Directional statistical significance test that has the critical region entirely in one tail of the distribution.
One-way ANOVA	An analysis of variance with only one independent variable; it compares the means of several groups to determine whether or not they are likely to come from the same population.
Operationalize	To define a construct in such a way that it can be measured and manipulated.
Ordinal	The level of measurement that represents rank, where the differences in value are not equal; ordinal data categories are mutually exclusive and exhaustive.
Orphan	A heading or subheading at the bottom of a page that is not followed by text…a line ending a paragraph at the top of a page. (See widow)
Outliers	Scores with standardized residuals greater than 2 (scores significantly more deviant than most scores).
P	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
p value	The probability or likelihood that an event will occur. In a statistical hypothesis test, the P value is the probability of observing a test statistic at least as extreme as the value actually observed, assuming that the null hypothesis is true. This probability is then compared to the pre-selected significance level of the test (alpha). If the p value is smaller than the significance level, the null hypothesis is rejected, and the test result is considered significant.
Paired sample t-test	A parametric statistical test used to determine whether there is a significant difference between the average values of the same measurement made with paired sets of data.  Both measurements are made on each subject or pair in the sample, and the results are based on the paired differences between these two samples.
Parameter	A number that describes a characteristic of a population.
Parametric statistical tests	Statistical tests that make assumptions about population parameters, and can be used with variables measured on interval or ratio scales.
Partial Correlation	In multivariate analysis, a partial correlation is a measure of the strength of the relationship between any two variables when the other variables are held constant.
Path analysis	A strategy for understanding causal processes through the analysis of correlational data.
Per-comparison error rate	The degree of risk assigned to any single dependent variable.
Per-comparison type II error rate	The probability of failing to reject the null hypothesis when the null hypothesis is false to some specified degree; the experiment-wise type II error rate (βEW) is the probability of failing to reject one or more false null hypotheses in a series of statistical tests.
Phenomenology	A qualitative method of research concerned with the basic structure of a phenomenon, using the first hand experience of the participants and/or the investigator.
Point-biserial correlation	A correlation between one continuous variable and a second variable with a natural dichotomy (e.g., male/female).
Population	All scores or members of a group that are of interest to a researcher; the group to which the researcher wishes to generalize.
Post hoc test	Statistical tests used to compare means AFTER the data have been examined to determine that there IS a significant difference between one or more pairs of means. The post hoc test then compares all the groups of means to look for significant differences, maintaining the integrity of the test and reducing the chance of making a type 1 error (rejecting the null hypothesis when it is true).
Power	The probability of not committing a type II error within a given test (1-ß)
Predictors	Independent variables used to predict criterion variables.
Probability	The likelihood that a statistical result was obtained by chance.
Q-R	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Qualitative variable	A nominal or ordinal scale variable; a variable for which different scores represent differences in kind or quality, not amount.
Qualitative research	Research methods designed to explain the significance and meaning of social phenomena with the least amount of interference in the natural setting as possible.
Quantitative variable	An ordinal, interval, or ratio-scale variable; a variable for which different scores represent amounts in the property being measured.
Quantitative research	Research methods that utilize descriptive and inferential statistical techniques.
Quasi-experimental research	Research methods designed to investigate possible cause-and-effect relationships, but, unlike the true experimental design, does not allow for the control and/or manipulation of all relevant variables. At least one variable is manipulated, but subjects are not randomly assigned to groups (without randomization, the researcher must identify and separate the effects of the treatments from the effects of all other factors affecting the dependent variable).
R	(Multiple correlation coefficient) correlation coefficient between one variable and linear combination of predictor variables.
r	(The correlation coefficient) a number that represents the intensity and direction of  relationship between two quantitative variables
Random sample	A random sample of size n is a collection of n objects where each member of the population is independent and has an equal chance of becoming part of the sample.
Random variables	Independent variables that may take alternative values according to chance.
Ratio	A level of measurement where numbers represent the distance between the values of a characteristic, and there is an absolute zero point (constant units of measurements are used), where zero represents an absence of the characteristic.  Data categories are mutually exclusive and exhaustive, are scaled according to the amount of the characteristic they possess.
Raw data	Ungrouped (unorganized, unanalyzed) data.
Refereed journal	A journal where the editor (the person in charge of the journal) sends papers submitted to the journal out for critical review usually to two different experts in the field of interest.
Regression	The ability to predict the score on one variable from the score of another; simple linear regression uses one dependent variable, and one independent variable; multiple regression uses multiple independent variables.
Regression coefficient	The slope b of a line obtained using the least squares fit of the line.
Regression toward the mean	The tendency for individuals selected because of extreme scores on one variable to have less extreme scores on any other variable.
Relative frequency	Another term for proportion; it is the value calculated by dividing the number of times an event occurs by the total number of times an experiment is carried out.
Relative frequency distribution	The fraction of the total number of observations in each class. To convert a frequency distribution to a relative frequency distribution, each of the class frequencies is divided by the total number of observations.
Reliability	The degree to which scores are free from errors of measurement. Estimates of reliability will differ, to a greater or lesser extent, depending on the specific sources of error being addressed
Repeated measures analysis of variance	(An extension of a dependent-samples t-test) a statistical procedure designed to separate out the effect of individual differences from the effect of time, measurement, or other variable that differentiates the groups.
Repeated measures design	A design in which each individual is measured more than once.
Research	Careful, systematic, patient investigation undertaken to discover or establish facts and relationships, and contribute to general knowledge.
Research methodology	The set of rules followed by a researcher when conducting a study.
Research question	Indicates the problem the researcher is attempting to solve.
Response bias	Error introduced into the study results because respondents tend to answer questions in a certain direction
Results	A summary of the data collected and the statistical or data analysis. The results section does not include any interpretation of the data or analysis.
Robust	A property of a statistical procedure that accurately estimates the probability of type 1 error even if the assumptions of the procedure are not completely met.
Running head	An abbreviated title at the top of the first page of an article or research paper to identify the article for readers. The running head is a maximum of 50 characters, counting letters, punctuation, and spaces between words.
S	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Sample	A subset of elements from a population. Those elements or subjects included in a given research study.
Sampling	Any of a number of procedures where the sample (the subset of elements from a population) are chosen.
Sampling error	Chance errors that occur during the process of selecting samples.
Scatterplot	A graph plotting the individual data points from a set of X-Y pairs.
Scientific method	The process of researching a problem, formulating a hypothesis and research question, determining a specific methodology to explore that problem, and using quantitative and qualitative procedures to analyze and interpret the data.
Secondary source	A document written by someone who did not conduct the research, develop the theory, or express the opinions that are discussed in an article or research paper.
Significance level	The likelihood of obtaining results as extreme as those observed for the sample when the null hypothesis is true; statistical significance indicates whether the differences between means are likely to have occurred by chance (e.g., ANOVA/t-test), or whether there are significant relationships or significant differences between two or more variables or levels of variables (e.g., regression).
Simple linear regression	Statistical procedure to find linear relationship between a criterion variable and a possible predictor variable by using the regression equation.
Simple Random Sampling	A sampling technique in which participants are randomly selected from the population, and all members of the population have an equal chance of being selected.
Single-sample t-test	Test for comparing the mean of a sample to a hypothetical value for μ (population mean).
Skewness	Lack of symmetry (positively skewed has many low scores and a right-handed tail; negatively skewed has many high scores and a left-handed tail). Data from a positively skewed (skewed to the right) distribution have values that are bunched together below the mean, but have a long tail above the mean.
Standard deviation	A measure of variability that is equal to the square root of the average squared deviation from the mean of a set of scores; the square root of the variance.
Standard error of estimate	The standard deviation of the differences between predicted scores and actual scores (the residuals).
Standardized coefficient	In regression analysis, the slope of the regression line is measured by coefficients. The standardized coefficient, represented by the Greek letter 'beta', is the slope of the regression line, measured in standardized units.
Statistic	A number that describes characteristic of a sample; it is symbolized by a letter from the English alphabet.
Statistically significant	Term used to describe an observed difference or relationship among variables that is unlikely to be due to chance.
Stem and Leaf	The "stem" is a column of the data with the last digit removed. The final digits of each column are placed next to each other in a row next to the appropriate column, and then each row is sorted in numerical order.
Stratified Sampling	A sampling technique involving the identification of important subgroups within the population, determining the proportion of each subgroup, and selecting the sample based on those proportions.
Sum of squares	The sum of the squared deviations of scores from the mean.
T-U	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Table	An efficient presentation of data (whether text, numerical information, or a combination) in a series of columns and rows.
Test of significance	A mathematical procedure allowing the researcher to determine if the null hypothesis can be rejected at a predetermined alpha level
t-test	A statistical significance test used to test hypotheses about one or two means when the population standard deviation is unknown.
Theory	An explanation of the commonalities and relationships among observed phenomena in terms of the causal structures and processes that are presumed to underlie them.
Treatment	Level of the independent variable in which subjects are exposed to some manipulation or experience; planned experimental manipulation.
Two-tailed significance test	Statistical significance test in which the critical region is divided equally between two tails.
Type 1 error	Rejection of the null hypothesis when it is true.
Type II error	Retention of the null hypothesis when it is false.
Univariate statistics	Analyses in which there is a single dependent variable.
Unstandardized coefficients	In regression analysis, the slope of the regression line is measured by coefficients. The unstandardized coefficient, represented by the letter 'b', is the slope of the regression line, measured in the same units as the independent variable.
V-Z	A B C D E F G-I L-M N-O P Q-R S T-U V-Z
Unit of analysis	The participant, subject, or individual organization or item you are analyzing.
Unstructured interviewing	An interview tecnique in which the researcher has no predetermined interview protocol; the questions develop as the interview progresses.
Validity	The correctness, meaningfulness, and applicability of the specific inferences made from study results. Test validation is the process of accumulating evidence to support such inferences. Validity measures are divided into three areas: content, criterion, and construct.
Variable	Characteristics of people, place, events or things that change, i.e., a measurement that can take on more than one value.
Variance	A measure of the variability of scores in a distribution equal to the average of the squared deviations of the scores around the mean; the square of the standard deviation.
Voluntary participation	An ethical requirement of research where the researcher ensures that study participants or subjects are not coerced in any way and may leave the study at any time without penalty.
Weighted index	A quantitative score used to measure a construct by applying a formula that combines relevant data where each data component is weighted differently, based on unique elements.
Widow	A short line ending a paragraph at the top of a page. (See orphan)
x-axis	The horizontal axis sometimes referred to as the abscissa, although the abscissa is more correctly the actual coordinates along the x-axis.
y-axis	The vertical axis sometimes referred to as the ordinate, although the ordinate is more correctly the actual coordinates along the y-axis.
z-score	Type of standard score equal to the raw score minus the mean divided by the standard deviation (a z distribution has a mean = zero and standard deviation = 1).

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