The AstroStat Slog » ARCH http://hea-www.harvard.edu/AstroStat/slog Weaving together Astronomy+Statistics+Computer Science+Engineering+Intrumentation, far beyond the growing borders Fri, 09 Sep 2011 17:05:33 +0000 en-US hourly 1 http://wordpress.org/?v=3.4 [MADS] ARCH http://hea-www.harvard.edu/AstroStat/slog/2009/mads-arch/ http://hea-www.harvard.edu/AstroStat/slog/2009/mads-arch/#comments Fri, 04 Sep 2009 18:30:27 +0000 hlee http://hea-www.harvard.edu/AstroStat/slog/?p=3477 ARCH (autoregressive conditional heteroscedasticity) is a statistical model that considers the variance of the current error term to be a function of the variances of the previous time periods’ error terms. I heard that this model made Prof. Engle a Nobel prize recipient.

Heteroscedesticity in regression problems in astronomy has been discussed with various kind of observations since astronomers are interested in correlations and causality between variables in the data set. Perhaps, the heteroscedasticity in volatilty of finance does not have any commonality with astronomical times series data, which could be the primary reason this celebrated model does not appear in ADS. However, there are various times series models branched from ARCH that consider heteroscedasticity in errors and I hope some can be useful to astronomers for analyzing times series data with inhomogeneous errors.

[Note] All links lead to wikipedia.org

]]>
http://hea-www.harvard.edu/AstroStat/slog/2009/mads-arch/feed/ 0
Change Point Problem http://hea-www.harvard.edu/AstroStat/slog/2007/change-point-problem/ http://hea-www.harvard.edu/AstroStat/slog/2007/change-point-problem/#comments Wed, 08 Aug 2007 21:14:49 +0000 hlee http://hea-www.harvard.edu/AstroStat/slog/2007/change-point-problem/ X-ray summer school is on going. Numerous interesting topics were presented but not much about statistics (Only advice so far, “use implemented statistics in x-ray data reduction/analysis tools” and “it’s just a tool”). Nevertheless, I happened to talk two students extensively on their research topics, finding features from light curves. One was very empirical from comparing gamma ray burst trigger time to 24kHz observations and the other was statistical and algorithmic by using Bayesian Block. Sadly, I could not give them answers but the latter one dragged my attention.

Recently I went to JSM 2007 and tried to attend talks about (bayesian) change point problems, which frequently appears in time series models, often found in economics. With ARCH (autoregressive conditional heteroskedecity) or GARCH (generalized ARCH) and by adding a parameter indicates a change point, I thought bayesian modeling could handle astronomical light curves.

Developing algorithms based on statistical theories, writing algorithms down in a heuristics way, making the code public, and finding/processing proper datum examples from huge astronomical data archives should come simultaneously, and this multiple steps make proposing new statistics to astronomical society difficult. I’m glad to know that there are individuals who are devoting themselves to make these steps happened. Unfortunately, they are loners.

]]>
http://hea-www.harvard.edu/AstroStat/slog/2007/change-point-problem/feed/ 4