On Fri, Aug 7, 2009 at 3:08 PM, Kevin Grittner<kevin.gritt...@wicourts.gov> wrote: > Sam Mason <s...@samason.me.uk> wrote: > >> All we're saying is that we're less than 90% confident that there's >> something "significant" going on. All the fiddling with standard >> deviations and sample sizes is just easiest way (that I know of) >> that statistics currently gives us of determining this more formally >> than a hand-wavy "it looks OK to me". Science tells us that humans >> are liable to say things are OK when they're not, as well as vice >> versa; statistics gives us a way to work past these limitations in >> some common and useful situations. > > Following up, I took the advice offered in the referenced article, and > used a spreadsheet with a TDIST function for more accurate results > than available through the table included in the article. That allows > what I think is a more meaningful number: the probability that taking > a sample that big would have resulted in a t-statistic larger than was > actually achieved if there was no real difference. > > With the 20 samples from that last round of tests, the answer (rounded > to the nearest percent) is 60%, so "probably noise" is a good summary. > Combined with the 12 samples from earlier comparable runs with the > prior version of the patch, it goes to a 90% probability that noise > would generate a difference at least that large, so I think we've > gotten to "almost certainly noise". :-)
So should we give up on this patch? ...Robert -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers