| confidence interval for a population parameter | Indicates the range of values in which we can expect a population value to fall with a specified degree of confidence (e.g., .95).
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| Confirming What the Data Tell Us | In the third stage of data analysis, the researcher determines what the data tell us about behavior. Statistical techniques are used to counter arguments that the results are simply “due to chance.”
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| correlation | Exists when two different measures of the same people, events, or things vary together; the presence of a correlation makes it possible to predict values on one variable by knowing the values on the second variable.
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| correlation coefficient | Statistic indicating how well two measures vary together; absolute size ranges from 0.0 (no correlation) to 1.00 (perfect correlation); direction of covariation is indicated by the sign of the coefficient, a plus (1) indicating that both measures covary in the same direction and a minus (2) indicating that the variables vary in opposite directions.
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| effect size | Index of the strength of the relationship between the independent variable and dependent variable that is independent of sample size.
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| estimated standard error of the mean | An estimate of the true standard error obtained by dividing the sample standard deviation by the square root of the sample size.
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| Getting to Know the Data | In this first stage of data analysis, the researcher inspects the data for errors and outliers and generally becomes familiar with the general features of the data.
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| linear trend | A trend in the data that is appropriately summarized by a straight line.
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| mean | The arithmetic mean, or average, is determined by dividing the sum of the scores by the number of scores contributing to that sum. The mean is the most commonly used measure of central tendency.
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| median | The middle point in a distribution, above which half the scores fall and below which half the scores fall.
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| meta-analysis | Analysis of results of several (often, very many) independent experiments investigating the same research area; the measure used in a meta-analysis is typically effect size.
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| mode | The score that appears most frequently in the distribution.
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| negative correlation | A relationship between two variables – as values for one measure increase, the values of the other measure decrease.
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| positive correlation | A relationship between two variables – as values for one measure increase, the values of the other measure also increase.
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| range | The difference between the highest and lowest number in a distribution.
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| scatterplot | A graph showing the relationship between two variables by indicating the intersection of two measures obtained from the same person, thing, or event.
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| standard deviation | The most commonly used measure of dispersion that indicates approximately how far on the average scores differ from the mean.
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| standard error of the mean | The standard deviation of the sampling distribution of means.
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| stem-and-leaf display | A technique for visualizing both the general features of a data set and specific item information by creating leading digits as “stems” and trailing digits as “leaves.”
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| Summarizing the Data | In this second stage of data analysis, the researcher uses descriptive statistics and graphical displays to summarize the information in a data set. Trends and patterns in the data set are described.
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