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  2. Kuder–Richardson formulas - Wikipedia

    en.wikipedia.org/wiki/Kuder–Richardson_formulas

    Often discussed in tandem with KR-20, is Kuder–Richardson Formula 21 (KR-21). [4] KR-21 is a simplified version of KR-20, which can be used when the difficulty of all items on the test are known to be equal.

  3. Geometric standard deviation - Wikipedia

    en.wikipedia.org/wiki/Geometric_standard_deviation

    The geometric standard deviation is used as a measure of log-normal dispersion analogously to the geometric mean. [3] As the log-transform of a log-normal distribution results in a normal distribution, we see that the geometric standard deviation is the exponentiated value of the standard deviation of the log-transformed values, i.e. = ⁡ (⁡ (⁡)).

  4. Sigma - Wikipedia

    en.wikipedia.org/wiki/Sigma

    The letter Sigma. Sigma (/ ˈ s ɪ ɡ m ə / SIG-mə; [1] uppercase Σ, lowercase σ, lowercase in word-final position ς; Ancient Greek: σίγμα) is the eighteenth letter of the Greek alphabet.

  5. Chemical formula - Wikipedia

    en.wikipedia.org/wiki/Chemical_formula

    A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs.

  6. Sheryl Sandberg - Wikipedia

    en.wikipedia.org/wiki/Sheryl_Sandberg

    Sandberg was born in 1969 in Washington, D.C., into a Jewish family. [11] [12] She is the eldest of three children, born to Adele (née Einhorn) and Joel Sandberg.[2] [13] Her father is an ophthalmologist, while her mother, a college professor of French, has roots tracing back to Belarus, as her grandparents were immigrants from there..