in Data-->statistics-->Descriptive Statistics, please add FIRST and THIRD Quartile to the list of reported statistical measures. For this the relevant function =QUARTILE() already exists in Calc
Eike/Winfried: I found a start here to implement it: http://opengrok.libreoffice.org/xref/core/sc/source/ui/StatisticsDialogs/DescriptiveStatisticsDialog.cxx#39 but should ux team give its advice about it? Meanwhile, I put it as new enhancement.
Tomaž Vajngerl committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=817b0b51e78b6870379f595a1f370985179847df fdo#81801 add first and third quartile to "Descriptive Statistics" It will be available in 4.4.0. The patch should be included in the daily builds available at http://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More information about daily builds can be found at: http://wiki.documentfoundation.org/Testing_Daily_Builds Affected users are encouraged to test the fix and report feedback.