Formula reference—Chi-squared, sample standard deviation, standard error and 95% CI

Apply the provided formulae to calculate a statistic, then interpret the size or interval rather than memorising symbols in isolation.

Keep observed and expected values paired and preserve units for biological quantities.

A confidence interval around a mean expresses uncertainty in that estimate, not the full spread of individual observations.

A correct calculation can still be misinterpreted if degrees of freedom or the null hypothesis is wrong.