R.QBETA Function (Gnumeric)

• Introduced: First release not established; named in Gnumeric 1.12.9 release notes.
• Supported in: Gnumeric 1.12.62; no retirement is established.
• Scope: Desktop Gnumeric with its Statistical Functions From R plugin. English comma-separated formulas are shown.
• Checked: October 14, 2026. Tables and the named advanced check use 1.12.57 ssconvert. Current 1.12.62 source was inspected; that release was not executed.

R.QBETA finds a cutoff on [0,1] for a specified beta probability. By default it solves P(X≤x)=probability; with lower_tail FALSE it solves P(X>x)=probability. Both alpha and beta are shape parameters, despite the second parameter’s “scale” label in generated help. Versioned function help.

=R.QBETA(probability,alpha,beta[,lower_tail[,log_p]])

• probability: normally from 0 through 1; supply its natural logarithm when log_p is TRUE.
• alpha, beta: required, strictly positive for a continuous beta model.
• lower_tail: optional, defaults to TRUE.
• log_p: optional, defaults to FALSE. The returned cutoff itself is not logged.

Brackets mark optional arguments; do not type them. Current worksheet implementation.

These self-contained formulas were recalculated natively. Ordinary-domain results were checked against independent mathematics; invalid-model observations are identified separately below. Results are rounded to twelve decimal places, or thirteen significant digits for small nonzero values. This is presentation precision, not a universal accuracy guarantee.

For shapes 2,3, the lower quartile is approximately 0.243022083756 and the upper quartile is 0.543678285419. The latter can be requested either with lower-tail probability 0.75 or upper-tail probability 0.25.

For Beta(1,4), =R.QBETA(0.3,1,4) gives approximately 0.085308780771. The closed form 1-(1-0.3)^(1/4) provides a separate check for this particular shape pair.

Use =R.QBETA(LN(0.25),2,3,FALSE(),TRUE()) when the supplied number is a log upper-tail probability. Passing LN(0.25) without log_p=TRUE instead supplies a negative ordinary probability and is invalid.

For positive shapes, feeding the returned cutoff into the matching lower-tail R.PBETA recovers the requested probability within numerical precision. The saved advanced check targets 0.75. This identity requires the same shapes and tail convention on both sides.

The saved advanced-check result for =R.PBETA(R.QBETA(.75,2,3),2,3) was 0.75.

Valid positive shapes give cutoffs 0 and 1 at ordinary lower-tail probabilities 0 and 1. With log_p=TRUE, input 0 means log(1), so the cutoff is 1, not 0. A positive log-probability is invalid.

The zero-shape rows are retained as native observations only. =R.QBETA(0.5,2,0) returned approximately 0.12132034356, although beta=0 is outside the positive-shape continuous model. Negative shapes produced #NUM!; zero shapes are not rejected by the same guard. Validate them yourself. A blank probability becomes zero and therefore returns the lower endpoint.

F5 is genuinely empty, rather than a cell containing an empty string. #NUM! can represent an unrepresentable infinite mathematical endpoint as well as an invalid numeric domain; the distinctions above matter.

• Current worksheet callback
• Tested-version worksheet callback
• Current qbeta calculation
• Tested-version qbeta calculation
• Nonfinite worksheet-value handling
• Statistical Functions From R plugin declaration

The relevant complete worksheet callback and main calculation helper are unchanged between the inspected versions. That does not establish later-version numerical execution. Both stale and uncached SUM controls recalculated correctly. Native XML identities were checked; secondary ODF exports retain these functions with the ORG.GNUMERIC namespace. GUI entry, other locales and other spreadsheet products were not tested.

BETAINV, BETADIST, LN.