Term
| Alpha (Level of Significance) |
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Definition
| Refers to the probability of rejecting the null hypothesis when it is true; ie. the probability of making a Type I error. The value is set by an experimenter prior to collecting or analyzing the data. it is commonly set at either .01 or .05. |
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Term
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Definition
| Analysis of covariance. A version of the ANOVA used to increase the efficiency of the analysis by statistically removing variability in the DV that is due to an extraneous variable. When using this, each person's score on the DV is adjusted on the basis of her score on teh extraneous variable. |
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Term
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Definition
| A disadvantage of the time-series and other within-subjects designs is that the analysis of the data can be confounded by this, whihc occurs when subjects' performance on the post-tests is likely to correlate with their performance on the pretests. Autocorrelation can inflate the value of the inferential statistic (eg. the t or F), thereby resulting in an increased probability of a Type I error. |
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Term
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Definition
| Studies in which the effects of the different levels of one or more IVs are compared by administering each level or combination of levels to a different group of participants. |
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Term
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Definition
| Derived from probability theory that predicts that the sampling distribution of the mean (1) will approach a normal shape as the sample size increases, regardless of the shape of the population distribution of scores; (2) has a mean equal to the population mean; and (3) has a standard deviation equal to the population standard deviation divided by the square root of the sample size. |
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Term
| Chi-Square Tests/Single-sample and Multiple Sample |
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Definition
| Inferential statistical tests used when teh data to be analyzed represent a nominal scale. The singel-sample chi-square test is used when the study includes one variable; the multiple-sample chi-square test when it includes two or more variables. |
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Term
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Definition
| In contrast to other forms of sampling (which involve selecting individuals from the population), cluster sampling entails selecting units or groups (clusters) of individuals from the population (eg. schools, hospitals). |
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Term
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Definition
| A numerical index of the relationship (degree of association) between two or more variables. Teh magnitude indicates the strength of the relationship; its sign indicates the direction (+ or -). |
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Term
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Definition
| Used when data on both variables represent a continuous scale; |
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Term
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Definition
| Used when one variable is a true dichotomy and the other is continuous |
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Term
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Definition
| Used when one variable is an artificial dichotomy and the other is continuous |
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Term
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Definition
| Used when the variables are continuous but have a nonlinear relationship. |
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Term
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Definition
| A research design used to control carryover (order) effects; involves administering the different levels of the IV to different subjects or groups of subjects in a different order. The Latin square design is a type of this. |
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Term
| Cross-Validation/Shrinkage |
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Definition
| Refers to validating a correlation coefficient (eg. a criterion-related validity coefficient) on a new sample. Because the same chance factors operating the original sample are not operating in the subsequent sample, the correlation coefficient tends to "shrink" on this. In terms of the multiple correlation coefficient (R), shrinkage is greatest when the original sample is small and the number of predictors is large. |
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Term
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Definition
| Cues in the experimental situation that inform research participants of how they are expected to behave during the course of the study. Can threaten a study's internal and external validity. |
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Term
| Discriminant Function Analysis |
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Definition
| The multivariate technique used when there are two or more continuous predictors and one discrete (nominal) criterion. Referred to as multiple discriminant function analysis when teh cirterion has more than two categories. |
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Term
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Definition
| Involves conducting a study to test hypotheses about the relationships between independent and dependent variables. |
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Term
| Experimentwise Error Rate |
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Definition
| Refers to the probability of making a Type I error. As the number of statistical comparisons in a study increases, the experimentwise error rate also increases. |
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Term
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Definition
| The degree to which a study's results can be generalized to toher people, setings, conditions, etc. |
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Term
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Definition
| Used when a study includes 2 or more IVs (ie. when the study has used a factorial design). Also referred to as a two-way, three-way, etc, with the number referring to the number of IVs. |
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Term
| Factorial Design/Main effects and Interaction |
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Definition
| The name given to any research design that includes two or more "factors" (independent variables). Factorial designs permit analysis of main and interaction effects. A main effect is the effect of a single IV on the DV. An interaction occurs when the impact of an IV differs at different levels of another IV. |
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Term
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Definition
| Manipulated in a research study for the purpose of determining its effects on teh dependent variable; the variable that is believed to have an effect on the dependent variable. Each one must have at least two levels. |
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Term
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Definition
| Observed and measured in a study and is believed to be affected by the independent variable. |
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Term
| Internal Validity/Maturation, History, Selection |
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Definition
| The degree to which a research study allows an investigator to conclude that observed variability in a dependent variable is due to the independent variable rather than to other factors. Maturation is one threat to this. It occurs when a physical or psychological process or event occurs as the result of the passage of time and has a history, which refers to an event that is external to a research study and that is not relevant to the research hypothesis but that affects subjects' performance on the dependent variable in a systematic way and thereby confounds the results of the study. Selection threatens internal validity when participants in different treatment groups are initially different and, therefore, would differ at the end of the study even if no treatment had been applied. Selection is a threat when participants are not randomly assigned to groups. |
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Term
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Definition
| A method of behavioral sampling that involves dividing a period of time into discrete intervals and recording whether the behavior occurs in each interval. It is particularly useful for behaviors that have no clear beginning or end. |
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Term
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Definition
| A method of behavioral sampling that is useful for behaviors that are rare or that leave a permanent product. It involves recording each occurrence of a behavior during a predefined or preselected event. |
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Term
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Definition
| A causal (structural equation) modeling technique used to verify a predefined causal model or theory. More complex than path analysis; it allows two-way (non-recursive) paths and takes into account observed variables, the latent traits they are believed to measure, and the effects of measurement error. |
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Term
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Definition
| Multivariate Analysis of Variance. A form of the ANOVA used when a study includes one or more IVs and two or more DVS, each of which is measured on an interval or ratio scale. Use of this helps reduce the experimentwise error rate and increases power by analyzing the effects of the IV on all DVs simultaneously. |
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Term
| Measures of Central Tendency/Mean, Median, Mode |
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Definition
| The mean is the arithmetic average of a set of scores. The mean can be used when scores are measured on an interval or ratio scale. The median is the middle score in a distribution of scores when scores have been ordered from lowest to highest. It is used with ordinal data (and often with interval and ratio data when the distribution is skewed or contains one or a few outliers). Finally, the mode is the value (score or category) that occurs most frequently in a distribution of nominal categories. |
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Term
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Definition
| Research designs in which both between groups and within subjects comparisons can be made. |
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Term
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Definition
| The multivariate technique used for predicting a score on a continuous criterion based on performance on two or more continuous and/or discrete predictors. Ideally, predictors included in a multipl regression equation will have low correlations with each other and high correlations with the criterion. (High correlations between predictors is referred to as a multicollinearity.) The output of multiple regression is the multiple correlation coefficient and multiple regression equation. |
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Term
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Definition
| A symmetrical bell-shaped distribution that is defined by a specific mathematical formula. When scores on a variable are normally-distributed, it is possible to conclude that a specific number of observations fall within certain areas of that distribution that are defined by the standard deviation: In a normal distribution, about 68% of observations fall between the scores that are plus and minus one SD from the mean. 95% between the scores that are +/- 2SD from themean, and 99% are +/- 3SD from the mean. |
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Term
| Null and Alternative Hypotheses |
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Definition
| In experimental research, the investigator tests a verbal research hypothesis by simultaneously testing two competing statistical hypotheses. The first, is stated in a way that implies that the independent variable does not have an effect on the dependent variable. The second states the opposite of the null hypothesis. It is expressed in a way that implies that the independent variable does have an effect. |
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Term
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Definition
| A parametric statistical test used to compare the means of two or more groups when a study includes one independent variable and one dependent variable that is measured on an interval or ratio scale. It is preferable to multiple t-tests when a study involves more than 3 groups because it helps control the experimentwise error rate. It yields an F-ratio that indicates if any group means are significantly different. |
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Term
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Definition
| Represents a measure of treatment effects plus error divided by a measure of error only (MSB/MSW). When the treatment has had an effect, the F-ratio is larger than 1.0. |
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Term
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Definition
| Inferential statistical tests that are used when teh data to be analyzed represent an interval or ratio scale and when certain assumptions about the population distribution have been met: ie., when scores on the variable of interest are normally distributed and when there is homoscedasticity (population variances are equal). An advantage of the tests is that they are more powerful than the nonparametric tests. |
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Term
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Definition
| Inferential statistical tests used when teh data to be analzyed represent either an ordinal or nominal scale or when teh assumptions for a parametric test have not been met. Include teh chi-square tests, the Mann-Whitney U, and the Wilcoxon matched-pairs test. |
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Term
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Definition
| A causal modeling technique used to verify a pre-defined causal model or theory. Involves translating the theory into a path diagram, collecting data on the variables of interest (the observed variables), and calculating and interpreting path coefficients. |
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Term
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Definition
| Technique used by cognitive psychologists to identify the cognitions underlying problem-solving and decision-making. Involves having an individual "think aloud" while working and then analyzing the record (protocol) of the individual's verbalizations. |
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Term
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Definition
| Refers to a method of assigning subjects to treatment groups using a random method; sometimes referred to as "randomization." Considered the hallmark of true experiemental research because it enables an investigator to conclude that any observed effect of an IV is due to the IV rather than to error. |
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Term
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Definition
| Error that is unpredictable (random). Sampling error is a type of this. |
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Term
| Randomized Block Factorial Anova |
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Definition
| A version of the ANOVA that is appropriate when blocking has been used as a method for controllin gan extraneous variable. Allows an investigator to statistically analyze the main and interaction effects of the extraneous variable (which is being treated as an additional IV). |
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Term
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Definition
| A statistical technique used to predict a score on a criterion based on the person's obtained score on a predictor. INvolves the identification of a regression line (line of best fit) and the use of the equation for that line, the regression equation. |
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Term
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Definition
| Contains those sample values (eg. means) that are unlikely to be obtained simply as the result of sampling error. When an inferential statistical test indicates that the obtained sample value falls in the rejection region, the null hypothesis is rejected and the alternative hypothesis is retained. The size is defined by alpha. |
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Term
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Definition
| The region of a sampling distribution that contains those values that are likely to be obtained simply as the result of sampling error. When an inferential statistical test indicates that an obtained sample value is in this region, the null hypothesis is retained and the alternative hypothesis is rejected. This is equal to one minus alpha. |
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Term
| Sampling Distribution of the Mean |
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Definition
| The distribution of sample means that would be obtained if an infinite number of equal-size samples were randomly selected from the population and the mean for each sample calculated. This is normally-shaped, its mean is equal to the population mean, and it sstandard deviation (the standard error of the means) is equal to the population standard deviation divided by the square root of the samle size. Used in inferential statistics to determine how likely it is to obtain a particular sample mena given the population mena, the population standard deviation, the sample size, and the level of significance. |
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Term
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Definition
| A method of categorizing the various ways to measure variables. There are 4 scales that differ in terms of mathematical sophistication. From least to most sophisticated they are nominal, ordinal, interval, and ratio. A nominal scale yields frequency data; that is, the frequency of observations in each nominal ctegory. Ordinal, interval, and ratio scales yield scale values or scores. |
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Term
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Definition
| A correlation coefficient can be squared to obtain a measure of shared variability. For example, if the correlation between x and y is .50, this means that 25% of variability in Y is shared with variability in x. |
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Term
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Definition
| All contain at least one A (baseline) and one B (treatment) phase and include multiple measurements of the DV at regular intervals during each phase. The AB design includes a single baseline (A) phase and a single treatment (B) phase. The reversal design includes, at a minimum, two baseline phases and one treatment phase (an ABA or ABAB design). The treatment is withdrawn (reversed) during the second and subseuent baseline phases. Use of the multiple-baseline design involves sequentially applying a treatment to different baselines (eg. to different behavior, settings, or subjects). |
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Term
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Definition
| Asymmetrical distributions in which the majority of scores are located on one side of the distribution. In a positively skewed distribution, most scores are in teh low side but a few scores are in the high (positive) side of the distribution. In a negatively skewed distribution, the majority of scores are in teh hish side of the distribution, but a few are in the low (negative) side. "it's the tail that tells the tail. |
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Term
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Definition
| A measure of dispersion (variability) of scores around the mean of the distribution. Calculated by dividing the sum of the squared deviation scores by N (or N - 1) and taking the square root of the result. The square root of the variance. |
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Term
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Definition
| The probability of rejecting a false null hypothesis. Cannot be directly controlled but can be increased by including a large sample, maximizing the effects of the IV, increasing the size of alpha, and reducing error. |
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Term
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Definition
| A predictable error. Extraneous variables are a source of this. |
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Term
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Definition
| Parametric test used to compare two means. The single sample t test is used to compare a single obtained sample mean to a known or hypothesized population mean. The t test for independent samples is used to compare means from two independent samples. The t test for correlated samples is used to compare two sample means when subjects in teh two groups are related in some way (eg. because they were matched on an extraneous variable or because a single group pretest/posttest design was used). |
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Term
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Definition
| A type of analysis of variance used to assess linear and nonlinear trends when teh independent variable in quantitative. |
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Term
| Type I and Type II errors |
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Definition
| A type I error occurs when a true null hypothesis is rejected. The probability of making a Type I error is equal to alpha. A type II error occurs when a false null hypothesis is retained. The probability of making a Type II error is equal to beta (which is usually unknown). |
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Term
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Definition
| An experimental design in which each participant receives, at different times, each level of the IV (or combinations of the IVs) so that comparisons on the DV are made within participants rather than between groups. |
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