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  2. Standard deviation - Wikipedia

    en.wikipedia.org/wiki/Standard_deviation

    This means that most men (about 68%, assuming a normal distribution) have a height within 3 inches of the mean (66–72 inches) – one standard deviation – and almost all men (about 95%) have a height within 6 inches of the mean (63–75 inches) – two standard deviations. If the standard deviation were zero, then all men would share an ...

  3. 68–95–99.7 rule - Wikipedia

    en.wikipedia.org/wiki/68–95–99.7_rule

    For an approximately normal data set, the values within one standard deviation of the mean account for about 68% of the set; while within two standard deviations account for about 95%; and within three standard deviations account for about 99.7%. Shown percentages are rounded theoretical probabilities intended only to approximate the empirical ...

  4. Normal distribution - Wikipedia

    en.wikipedia.org/wiki/Normal_distribution

    If is a standard normal deviate, then = + will have a normal distribution with expected value and standard deviation . This is equivalent to saying that the standard normal distribution Z {\textstyle Z} can be scaled/stretched by a factor of σ {\textstyle \sigma } and shifted by μ {\textstyle \mu } to yield a different normal distribution ...

  5. Standard score - Wikipedia

    en.wikipedia.org/wiki/Standard_score

    Comparison of the various grading methods in a normal distribution, including: standard deviations, cumulative percentages, percentile equivalents, z-scores, T-scores. In statistics, the standard score is the number of standard deviations by which the value of a raw score (i.e., an observed value or data point) is above or below the mean value of what is being observed or measured.

  6. Random walk - Wikipedia

    en.wikipedia.org/wiki/Random_walk

    Here, the step size is the inverse cumulative normal distribution (,,) where 0 ≤ z ≤ 1 is a uniformly distributed random number, and μ and σ are the mean and standard deviations of the normal distribution, respectively. If μ is nonzero, the random walk will vary about a linear trend.

  7. Assumed mean - Wikipedia

    en.wikipedia.org/wiki/Assumed_mean

    In statistics, the assumed mean is a method for calculating the arithmetic mean and standard deviation of a data set. It simplifies calculating accurate values by hand. Its interest today is chiefly historical but it can be used to quickly estimate these statistics.

  8. Variance - Wikipedia

    en.wikipedia.org/wiki/Variance

    The unbiased estimation of standard deviation is a technically involved problem, though for the normal distribution using the term n − 1.5 yields an almost unbiased estimator. The unbiased sample variance is a U-statistic for the function ƒ ( y 1 , y 2 ) = ( y 1 − y 2 ) 2 /2, meaning that it is obtained by averaging a 2-sample statistic ...

  9. Three-point estimation - Wikipedia

    en.wikipedia.org/wiki/Three-point_estimation

    These values are used to calculate an E value for the estimate and a standard deviation (SD) as L-estimators, where: E = (a + 4m + b) / 6 SD = (b − a) / 6. E is a weighted average which takes into account both the most optimistic and most pessimistic estimates provided. SD measures the variability or uncertainty in the estimate.