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  2. Degrees of freedom (statistics) - Wikipedia

    en.wikipedia.org/wiki/Degrees_of_freedom...

    If the data points are normally distributed with mean 0 and variance , then the residual sum of squares has a scaled chi-squared distribution (scaled by the factor ), with n − 1 degrees of freedom. The degrees-of-freedom, here a parameter of the distribution, can still be interpreted as the dimension of an underlying vector subspace.

  3. Guttman scale - Wikipedia

    en.wikipedia.org/wiki/Guttman_scale

    The discovery of a Guttman scale in data depends on their multivariate distribution's conforming to a particular structure (see below). Hence, a Guttman scale is a hypothesis about the structure of the data, formulated with respect to a specified attribute and a specified population and cannot be constructed for any given set of observations.

  4. Triangular distribution - Wikipedia

    en.wikipedia.org/wiki/Triangular_distribution

    This distribution for a = 0, b = 1 and c = 0.5—the mode (i.e., the peak) is exactly in the middle of the interval—corresponds to the distribution of the mean of two standard uniform variables, that is, the distribution of X = (X 1 + X 2) / 2, where X 1, X 2 are two independent random variables with standard uniform distribution in [0, 1]. [1]

  5. Semantic differential - Wikipedia

    en.wikipedia.org/wiki/Semantic_differential

    Verhagen and colleagues introduce a framework to assist researchers in applying the semantic differential. The framework, which consists of six subsequent steps, advocates particular attention for collecting the set of relevant bipolar scales, linguistic testing of semantic bipolarity, and establishing semantic differential dimensionality.

  6. Level of measurement - Wikipedia

    en.wikipedia.org/wiki/Level_of_measurement

    Level of measurement or scale of measure is a classification that describes the nature of information within the values assigned to variables. [1] Psychologist Stanley Smith Stevens developed the best-known classification with four levels, or scales, of measurement: nominal, ordinal, interval, and ratio.

  7. Likert scale - Wikipedia

    en.wikipedia.org/wiki/Likert_scale

    Likert scale data can, in principle, be used as a basis for obtaining interval level estimates on a continuum by applying the polytomous Rasch model, when data can be obtained that fit this model. In addition, the polytomous Rasch model permits testing of the hypothesis that the statements reflect increasing levels of an attitude or trait, as ...

  8. API gravity - Wikipedia

    en.wikipedia.org/wiki/API_gravity

    The American Petroleum Institute gravity, or API gravity, is a measure of how heavy or light a petroleum liquid is compared to water: if its API gravity is greater than 10, it is lighter and floats on water; if less than 10, it is heavier and sinks.

  9. C-squares - Wikipedia

    en.wikipedia.org/wiki/C-squares

    C-squares (acronym for the Concise Spatial QUery And REpresentation System) is a system of spatially unique, location-based identifiers for areas on the surface of the earth, represented as cells from a latitude- and longitude-based Discrete Global Grid at a hierarchical set of resolution steps, obtained by progressively subdividing 10×10 degree World Meteorological Organization squares; the ...