Six guides that show the arithmetic by hand, the same formula each calculator on this site runs, worked on a small data set you can check with a pencil.
Standard deviation measures how spread out values are from the mean. Learn the formula, population vs sample SD, and walk through a step-by-step example.
Read →Mean is the average, median is the middle value, and mode is the most frequent value. Learn how to find each with worked examples and when to use which.
Read →A p-value is the probability of seeing your result (or more extreme) if the null hypothesis were true. Learn what it means, what 0.05 means, and common mistakes.
Read →Margin of error = z * sqrt(p*(1-p)/n). Learn the formula, how to find it for 95% confidence, and what a good margin of error looks like.
Read →A z-score measures how many standard deviations a value sits from the mean. Learn the formula, what different z-scores mean, and how to calculate yours.
Read →A 95% confidence interval is the sample mean plus or minus 1.96 times the standard error. Learn the formula, how to get 1.96, and what the interval really means.
Read →