Plain-English guides to help you plan, save, and decide with confidence.
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.
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