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  2. Standard deviation - Wikipedia

    en.wikipedia.org/wiki/Standard_deviation

    Standard deviation may be abbreviated SD or std dev, and is most commonly represented in mathematical texts and equations by the lowercase Greek letter σ (sigma), for the population standard deviation, or the Latin letter s, for the sample standard deviation.

  3. Sigma - Wikipedia

    en.wikipedia.org/wiki/Sigma

    In finance, σ is the symbol used to represent volatility of stocks, usually measured by the standard deviation of logarithmic returns. In accounting , Σ indicates the balance of invoice classes and the overall amount of debts and demands.

  4. Normal distribution - Wikipedia

    en.wikipedia.org/wiki/Normal_distribution

    About 68% of values drawn from a normal distribution are within one standard deviation σ from the mean; about 95% of the values lie within two standard deviations; and about 99.7% are within three standard deviations. [8] This fact is known as the 68–95–99.7 (empirical) rule, or the 3-sigma rule.

  5. Template:List of statistics symbols - Wikipedia

    en.wikipedia.org/wiki/Template:List_of...

    Definitions of other symbols: ... = sample 2 standard deviation = t statistic = degrees of freedom ¯ = sample mean of differences ...

  6. Variance - Wikipedia

    en.wikipedia.org/wiki/Variance

    The red population has mean 100 and variance 100 (SD=10) while the blue population has mean 100 and variance 2500 (SD=50) where SD stands for Standard Deviation. In probability theory and statistics , variance is the expected value of the squared deviation from the mean of a random variable .

  7. Greek letters used in mathematics, science, and engineering

    en.wikipedia.org/wiki/Greek_letters_used_in...

    Greek letters are used in mathematics, science, engineering, and other areas where mathematical notation is used as symbols for constants, special functions, and also conventionally for variables representing certain quantities. In these contexts, the capital letters and the small letters represent distinct and unrelated entities.

  8. Deviation (statistics) - Wikipedia

    en.wikipedia.org/wiki/Deviation_(statistics)

    The second standard deviation from the mean in a normal distribution encompasses a larger portion of the data, covering approximately 95% of the observations. Standard deviation is a widely used measure of the spread or dispersion of a dataset. It quantifies the average amount of variation or deviation of individual data points from the mean of ...

  9. Statistical significance - Wikipedia

    en.wikipedia.org/wiki/Statistical_significance

    In specific fields such as particle physics and manufacturing, statistical significance is often expressed in multiples of the standard deviation or sigma (σ) of a normal distribution, with significance thresholds set at a much stricter level (for example 5σ).