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Notation and symbols

Greek letter sigma, denoting sum of. ∑x is shorthand for
$$ \sum_{i=1}^{n}{x_i} $$
| x | absolute value of x
α probability of a Type I error; or level of hypothesis test, usually 0.05
β probability of a Type II error
χ2 value from the Chi-squared distribution, see Chi-squared table
CI confidence interval
CR coefficient of repeatability
DF degrees of freedom
F value from the F-distribution, see F-Distribution critical values table
K kappa
n or N      sample size
P probability of hypothesis
r Pearson correlation coefficient
rs Spearman rank correlation coefficient
R2 coefficient of determination
RSD relative standard deviation
s standard deviation
s2 variance
SD standard deviation
SEM standard error of the mean
t value from the t-distribution, see t-distribution table
z value from the Normal distribution, see Normal distribution table