Comments on: Quote of the Week, Aug 31, 2007 http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/ Weaving together Astronomy+Statistics+Computer Science+Engineering+Intrumentation, far beyond the growing borders Fri, 01 Jun 2012 18:47:52 +0000 hourly 1 http://wordpress.org/?v=3.4 By: vlk http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/comment-page-1/#comment-80 vlk Tue, 04 Sep 2007 19:56:02 +0000 http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/#comment-80 I think that part of the reason 3 sigma is not reliable in spectral analysis is because of the number of bins. In an HETG spectrum there are 8192 bins, so a 3 sigma threshold can leave you with about 10 false positives (well fewer because of the finite width of the line spread function, but you get the idea). And it only gets worse with 16384-bin LETG spectra. I think that part of the reason 3 sigma is not reliable in spectral analysis is because of the number of bins. In an HETG spectrum there are 8192 bins, so a 3 sigma threshold can leave you with about 10 false positives (well fewer because of the finite width of the line spread function, but you get the idea). And it only gets worse with 16384-bin LETG spectra.

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By: Aneta Siemiginowska http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/comment-page-1/#comment-79 Aneta Siemiginowska Tue, 04 Sep 2007 02:10:45 +0000 http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/#comment-79 Well, in astronomy unknown calibration or measurement's uncertainties make a 3 sigma result not so convincing. There have been many discussion about some 2-3 sigma deviations in the high resolution X-ray spectra as to whether these are true emission/absorption lines or just unknown calibration features. With our improved knowledge of instruments and better calibrations some of these 2-3 sigma features have disappeared and became a noise... Well, in astronomy unknown calibration or measurement’s uncertainties make a 3 sigma result not so convincing. There have been many discussion about some 2-3 sigma deviations in the high resolution
X-ray spectra as to whether these are true emission/absorption lines or just unknown calibration features. With our improved knowledge of instruments and better calibrations some of these 2-3 sigma features have disappeared and became a noise…

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By: vlk http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/comment-page-1/#comment-78 vlk Sun, 02 Sep 2007 17:33:19 +0000 http://hea-www.harvard.edu/AstroStat/slog/2007/quote-of-the-week-aug-31-2007/#comment-78 Well I wouldn't go so far as to say that astronomers don't believe in 3-sigma results -- that is usually the acceptable threshold for source detection after all! But yes, for anything out of the ordinary (i.e., That-Which-Cannot-Be-Repeated), the bar is set higher. But the funny thing is, while gatecrashing the JSM last month, I kept noticing how statisticians seem to be so gung ho on repeatability and replicability -- of the results, of the methods, even of the numbers. I almost wrote up a post about this apparent cultural difference, and then had second thoughts, thinking, nah, surely that must be simply anecdotal bias. Well I wouldn’t go so far as to say that astronomers don’t believe in 3-sigma results — that is usually the acceptable threshold for source detection after all! But yes, for anything out of the ordinary (i.e., That-Which-Cannot-Be-Repeated), the bar is set higher.

But the funny thing is, while gatecrashing the JSM last month, I kept noticing how statisticians seem to be so gung ho on repeatability and replicability — of the results, of the methods, even of the numbers. I almost wrote up a post about this apparent cultural difference, and then had second thoughts, thinking, nah, surely that must be simply anecdotal bias.

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