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Glossary Archives

Quartile

Quartile: The 1st, 2nd, and 3d quartiles are the 25th, 50th, and 75th percentiles respectively. Browse Other Glossary Entries

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Range

Range: Range is a measure of dispersion. It is defined as the difference between the highest and the lowest values. Browse Other Glossary Entries

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Rank Correlation Coefficient

Rank Correlation Coefficient: Rank correlation is a method of finding the degree of association between two variables. The calculation for the rank correlation coefficient the same as that for the Pearson correlation coefficient, but is calculated using the ranks of the observations and not their numerical values. This method is...

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Root Mean Square

Root Mean Square: Root mean square (RMS) of a set of values xi, i=1,...N is the square root of the mean of the squares of the values:   RMS(x1, ... ,xN) =   ÃƒÂ¦ Ö  1 N N ? i=1  xi2 RMS is a statistical measure of departure from the null...

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Scatter Graphs

Scatter Graphs: A scatter graph shows the joint distribution of observed values of two variables. Each pair of values is shown as a point on X-Y plane with coordinates (Xi,Yi), where Xi and Yi are the values of the first and the second variable. Scatter graphs help draw attention to...

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Sequential Icon Plots

Statistical Glossary Sequential Icon Plots: Sequential icon plots (or column icon plots) are a category of icon plots . For each unit, variables are represented as a sequence of bars with the height reflecting the value of the corresponding variable. Besides the order in the sequence, colors are usually used...

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Similarity Matrix

Similarity Matrix: Similarity matrix is the opposite concept to the distance matrix . The elements of a similarity matrix measure pairwise similarities of objects - the greater similarity of two objects, the greater the value of the measure. For example, the correlation matrix often may be considered as as a...

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Skewness

Skewness: Skewness measures the lack of symmetry of a probability distribution. A curve is said to be skewed to the right (or positively skewed) if it tails off toward the high end of the scale (right tail longer than the left). A curve is skewed to the left (or negatively...

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Standard Deviation

Standard Deviation: The standard deviation is a measure of dispersion. It is the positive square root of the variance. An advantage of the standard deviation (as compared to the variance) is that it expresses dispersion in the same units as the original values in the sample or population. For example,...

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Standardized Mean Difference

Standardized Mean Difference: The standardized mean difference is the difference between two normalized means - i.e. the mean values divided by an estimate of the within-group standard deviation . The standardized mean difference is used for comparison of data obtained at different scales. Browse Other Glossary Entries

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Stanine

Statistical Glossary Stanine: A stanine is a "standard ninth," an interval used in dividing school test results into (more or less) ninths. Stanine 1 includes all scores less than 1.75 standard deviations below the mean, and stanine 9 all scores more than 1.75 standard deviations above the mean. Stanines 2-8...

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Star Icon Plots

Statistical Glossary Star Icon Plots: Star icon plots are a subclass of circular icon plots in which the rays tend to form a star. Browse Other Glossary Entries

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Sun Ray Plots

Statistical Glossary Sun Ray Plots: Sun ray plots are a subclass of circular icon plots in which the rays tend to form a circle. Browse Other Glossary Entries

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Survival Function

Survival Function: In medical statistics, the survival function is a relationship between a proportion and time. The proportion is the proportion of subjects who are still surviving at time "t." The term can also be applied in fields other than medicine, referring to "units still operating" rather then subjects still...

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The Tukey Mean-Difference Plot

Statistical Glossary The Tukey Mean-Difference Plot: The Tukey mean-difference plot is a scatter graph produced not for (x,y) values themselves, but for modified coordinates (X,Y)   X =  (x+y) 2 , Y = y-x. Such a plot is useful, for example, to analyze data with strong correlation between x and...

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Variance

Variance: Variance is a measure of dispersion. It is the average squared distance between the mean and each item in the population or in the sample. An advantage of variance (as compared to the related measure of dispersion - the standard deviation) is that the variance of a sum of...

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Variance/Mean Ratio

Statistical Glossary Variance/Mean Ratio: Variance/mean ratio (VMR) is used to characterize the distribution of events or objects in time or space. If the distribution is random - i.e. can be modeled by the Poisson process or its multidimensional analogues - then, the VMR is about 1.0. Larger values (VMR >1.0)...

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Asymptotic Efficiency

Asymptotic Efficiency: For an unbiased estimator, asymptotic efficiency is the limit of its efficiency as the sample size tends to infinity. An estimator with asymptotic efficiency 1.0 is said to be an "asymptotically efficient estimator". Roughly speaking, the precision of an asymptotically efficient estimator tends to the theoretical limit as...

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