From patchwork Sat Jun 27 15:08:05 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Lespiau, Damien" X-Patchwork-Id: 6685161 Return-Path: X-Original-To: patchwork-intel-gfx@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id AA6A5C05AC for ; Sat, 27 Jun 2015 15:08:57 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id EB7C520761 for ; Sat, 27 Jun 2015 15:08:56 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id 7C8D020773 for ; Sat, 27 Jun 2015 15:08:54 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 0528D6E734; Sat, 27 Jun 2015 08:08:53 -0700 (PDT) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by gabe.freedesktop.org (Postfix) with ESMTP id 543276E729 for ; Sat, 27 Jun 2015 08:08:48 -0700 (PDT) Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga101.jf.intel.com with ESMTP; 27 Jun 2015 08:08:48 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.13,689,1427785200"; d="scan'208";a="515137062" Received: from kczmudzi-mobl4.amr.corp.intel.com (HELO strange.ger.corp.intel.com) ([10.252.53.243]) by FMSMGA003.fm.intel.com with ESMTP; 27 Jun 2015 08:08:47 -0700 From: Damien Lespiau To: intel-gfx@lists.freedesktop.org Date: Sat, 27 Jun 2015 16:08:05 +0100 Message-Id: <1435417696-28115-8-git-send-email-damien.lespiau@intel.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1435417696-28115-1-git-send-email-damien.lespiau@intel.com> References: <1435417696-28115-1-git-send-email-damien.lespiau@intel.com> Subject: [Intel-gfx] [PATCH i-g-t 07/18] stats: Add a note about the standard deviation derived from unbiased variance X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" X-Spam-Status: No, score=-5.6 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Signed-off-by: Damien Lespiau --- lib/igt_stats.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/lib/igt_stats.c b/lib/igt_stats.c index 12cabba..bd05550 100644 --- a/lib/igt_stats.c +++ b/lib/igt_stats.c @@ -121,6 +121,11 @@ bool igt_stats_is_population(igt_stats_t *stats) * [Bessel's correction](https://en.wikipedia.org/wiki/Bessel%27s_correction) * to the variance. * + * Note that even if we manage to have an unbiased variance by multiplying + * a sample variance by the Bessel's correction, n/(n - 1), the standard + * deviation derived from the unbiased variance isn't itself unbiased. + * Statisticians talk about a "corrected" standard deviation. + * * When giving #true to this function, the data set in @stats is considered a * full population. It's considered a sample of a bigger population otherwise. *