@spec boxplot_stats([number()], number()) :: map()

Computes a box-plot summary — quartiles plus Tukey fences for whisker endpoints. Outliers are observations beyond 1.5·IQR (default).

Returns %{min, q1, median, q3, max, outliers} where min/max are the whisker endpoints (not the raw extrema — those are captured in :outliers).

iex> s = Bland.Stats.boxplot_stats([1, 2, 3, 4, 5, 6, 7, 100])
iex> {s.median, length(s.outliers)}
{4.5, 1}

@spec normal_quantile(number()) :: float()

Inverse standard-normal CDF (probit). Uses the Beasley-Springer / Moro approximation — accurate to about 1e-9 across the usual range.

iex> abs(Bland.Stats.normal_quantile(0.5)) < 1.0e-9
true

iex> Float.round(Bland.Stats.normal_quantile(0.975), 4)
1.96

@spec quantile([number()], number()) :: float()

Linearly-interpolated quantile (type-7, R's default). p is in [0, 1].

iex> Bland.Stats.quantile([1, 2, 3, 4, 5], 0.5)
3.0