R.QCHISQ Function (Gnumeric)

• Introduced: First release not established; present in the retained 1.12.57 source.
• 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.QCHISQ returns a chi-square quantile, using lower-tail probability by default. With lower_tail FALSE it returns a cutoff for the specified right-tail probability. Degrees of freedom may be positive real values. Versioned function help.

=R.QCHISQ(probability,degrees_freedom[,lower_tail[,log_p]])

• probability: ordinary probability from 0 to 1, or its natural logarithm when log_p is TRUE.
• degrees_freedom: required and positive; not truncated to an integer.
• lower_tail, log_p: optional TRUE and FALSE respectively. The result remains an ordinary cutoff.

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 4 degrees of freedom, the lower-tail 95th percentile is approximately 9.487729036781. Request the same upper-tail 5% cutoff with =R.QCHISQ(0.05,4,FALSE()). This is the tail setting needed for a conventional right-tail 5% critical value.

For 2 degrees of freedom, the lower-tail 95th percentile is approximately 5.991464547108. The closed form -2*LN(1-0.95) provides a separate mathematical check in this particular case.

A central 90% interval for the distribution of X itself uses lower-tail probabilities 0.05 and 0.95. It is not automatically a confidence interval for an unknown variance; that requires an appropriate model, sample variance and the reciprocal-quantile construction.

The saved advanced check compares the 4-degree 95th percentile with a gamma quantile using shape=2 and scale=2. A logged upper-tail input, LN(0.05) with FALSE and TRUE as the last two arguments, gives the same cutoff as the ordinary upper-tail call.

The saved advanced-check result for =R.QCHISQ(.95,4)-R.QGAMMA(.95,2,2) was 0.

Zero and negative degrees of freedom are rejected by this inverse, even though some related density/CDF functions contain zero-degree limit branches. Do not assume the family shares identical input guards.

For positive degrees, lower-tail probability 0 gives zero and probability 1 gives an infinite cutoff, displayed as #NUM!. Upper-tail endpoints reverse these outcomes. Log input 0 means probability 1; a positive log-probability is invalid. A blank probability becomes zero, which is a valid finite lower endpoint, not a missing-data warning.

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 qchisq calculation
• Tested-version qchisq calculation
• Current qgamma calculation
• Tested-version qgamma 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 preserves the R.* identities. Secondary ODF export maps two-argument R.DCHISQ to CHISQDIST with FALSE, R.PCHISQ to CHISQDIST, and R.QCHISQ to CHISQINV; additional arguments retain ORG.GNUMERIC names. These storage mappings do not establish execution in another product. GUI entry, other locales and other spreadsheet products were not tested.

CHIINV, CHIDIST, GAMMAINV.