The AstroStat Slog

My first impression from the 212th AAS meeting is that it’s planned for preparing IYA 2009 and many talks are about current and future project reviews and strategies to reach public (People kept saying to me that winter meetings are more grand with expanded topics). I cannot say I understand everything (If someone says no astronomers understand everything, I’ll be relieved) but thanks to the theme of the meeting, I was intelligently entertained enough in many respects. The downside of this intellectual stimulus is growing doubts. One of those doubts was regression analysis in astronomy.

I’m not going to name the session, the speaker, nor the topic. Only relevant story related to regression analysis.

One of sessions, a speaker showed a slide with a headline, … test H_o…. My expectation was that H_o indicated a null hypothesis related to the expansion of the universe so that he was going to do a hypothesis testing. I was wrong. This H_o was the Hubble constant and his plan was estimating it with his carefully executed astrometry.

After a few slides later, I saw a straight line overplotted on top of scattered points. If I dissect the given space into 4×4, the most of points were occupied in the lower left corner section, and there was only one point placed in the section of the upper right corner. This single point had the most leverage that determines the slope of the line. Without verification, such as using Cook’s distance, I wondered what would happen with the estimated slope. Even with that high leverage point, I wondered if he still could claim with real statistics that his slope (H_o) estimate prefers the model by Freedman to the model by Sandage? To my naive eyes, the differences between the estimated slope from data and the two theoretical slopes are hardly distinguishable.

I saw papers in astronomy/astrophysics that carefully explain caveats of regression analysis on their target data and describe statistical tests to show the differences and similarities. Probably, the speaker didn’t want to disturb the audience with boring statistics. Yet, this was one of the occasions where my doubts toward astronomers who practice statistics in their own ways without consulting scholarly works in statistics sufficiently. The other likelihood is that I myself is biased to see things. I bet I’m the only one who expected that …test H_o… would accompany a null hypothesis and hypothesis tests, instead of estimating the Hubble constant.