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Statistics calculators and tools

Probability, z-score, confidence interval, and sample-size calculators.

Probability CalculatorCalculate independent probability for A and B, A or B, and not A.Z-Score CalculatorCalculate z-score, approximate percentile, and distance from the mean.Confidence Interval CalculatorEstimate a confidence interval for a sample mean from mean, standard deviation, sample size, and confidence level.Sample Size CalculatorEstimate survey sample size from confidence level, margin of error, and population proportion.Standard Error CalculatorCalculate standard error and an approximate 95% margin from standard deviation and sample size.Weighted Average CalculatorCalculate a weighted average from three values and their weights.Binomial Probability CalculatorCalculate exact and at-least binomial probability from trials, successes, and success probability.Poisson Probability CalculatorCalculate exact and at-most Poisson probability from average event rate and event count.Chi-Square CalculatorCalculate a simple chi-square statistic from observed and expected counts.Correlation Coefficient CalculatorCalculate Pearson correlation from five x-y data pairs.

Describe the data before interpreting statistics

Statistics calculators summarize samples, probabilities, distributions, and relationships. Before entering numbers, define the population, variable, and sampling method. Mean, median, standard deviation, correlation, and probability answer different questions, so choose the measure that matches the shape of the data and the decision being made.

A precise output does not remove bias, missing data, outliers, or a weak sample. Inspect the observations, report sample size, and distinguish association from causation. For formal research, verify assumptions such as independence, distribution shape, and the selected significance level.