tag:blogger.com,1999:blog-5337555368793819627.post3071184663887934287..comments2023-06-07T09:04:36.390-04:00Comments on More Grumbine Science: Assessing predictionsRobert Grumbinehttp://www.blogger.com/profile/10783453972811796911noreply@blogger.comBlogger8125tag:blogger.com,1999:blog-5337555368793819627.post-89131610626036205642009-10-10T10:43:33.330-04:002009-10-10T10:43:33.330-04:00I'll be taking up some of this more in a full ...I'll be taking up some of this more in a full post. Some brief comments.<br /><br />Jesus: The reason for a distribution vs. a very narrow curve (it won't be exactly a line because the observations have some uncertainties to them, and that means a width to the curve) is that to start with I'm looking at climate. In such a view, what actually happens in any particular year is a sample from climate -- there could have been more or less than we observed this time, and that would be within climate variation. As a weather forecast, we'd be checking against the much narrower curve.<br /><br />Deciding what 'climatology' means, when you don't have much data in the first place, is a real problem. We know now, for instance, that there is a declining trend to the ice cover. But it is usual to consider climate a stable number. Given that the second half of the record is markedly not like the first half, we can't make that assumption. What I did was to take a part of the satellite record for which you <i>could</i> say there was no trend, and use that for the 'unchanging' part. It's about 15 years. 1979-1996 is the last span of the satellite record for which you could say the trend (from 1979 to that date) was not statistically significant (at 5% level). <br /><br />crandles: <br />Since there are still people saying that the sea ice has recovered, or will soon, and the recovery is to 1980s levels, while I agree that the given null forecaster is particularly stupid, I'll say that it is not unreasonably stupid. Granted those people are usually not scientists. Still, this is a blog rather than a journal article.<br /><br />Usual null forecasters are climatology (taken as a constant value, not a trend line), and persistence (this day/month/year will be like the last one). It's interesting to me that climatology is taken to have no trend. At this point, we certainly do expect change in sea ice extent. At least most of 'we' in the field do. Still, that is the norm.<br /><br />Having spotted a trend, you could also continue it. That is only marginally simpler than what I did do. As far as this sort of consideration goes, the suggestion would be that my approach is a slightly better null forecaster than the straight line. The methods which would use this as a null are the coupled atmosphere-ocean-ice models.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-60704080751057899042009-10-10T05:59:09.501-04:002009-10-10T05:59:09.501-04:00How simple should the null forcaster be?
It seem...How simple should the null forcaster be? <br /><br />It seems rather obvious that if you want to claim skill for your forecast then you make the null forecaster particularly stupid. <br /><br />This example of setting null forecaster to 'what normally happens' and making that the average of first 15 years of satellite era seems to be doing precisely that.<br /><br />I would go further than Jesus's comment:<br /><br />Spotting a trend and assuming that it will continue is easy and I suspect most people would include that in 'what normally happens'.<br /><br />"You always want your prediction to do better than the null forecaster. Otherwise, people could do as well or better with far less effort than you're putting in."<br /><br />Well of course you always want your prediction to do better that goes without saying. Surely, it may not always be possible to do better, but you want your prediction to be expected to be closer else your prediction is not doing anything useful.crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-24013761018585169102009-10-06T05:51:58.480-04:002009-10-06T05:51:58.480-04:00Are random dudes on the internet null forecasters?...Are random dudes on the internet null forecasters? Here is how they did:<br />http://lablemminglounge.blogspot.com/2009/10/arctic-sea-ice-prognosticator-of-year.htmlC W Mageehttps://www.blogger.com/profile/09706100504739548720noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-35323152731828877312009-10-05T15:33:04.150-04:002009-10-05T15:33:04.150-04:00I put both the 5.36 and the 5.4 figures on both of...I put both the 5.36 and the 5.4 figures on both of your blogs with a link to the data. I am looking forward to your next sea ice posts where I am expecting you both to claim victory ;)crandleshttps://www.blogger.com/profile/15181530527401007161noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-50844293038152749092009-10-05T14:51:01.892-04:002009-10-05T14:51:01.892-04:00In a different thread a reader gave the NSIDC link...In a different thread a reader gave the NSIDC link -- 5.36 million km^2. Much closer than I thought it would be, but it squeaks under our dividing line of 5.38. You lost this one. From your earlier posts at stoat, though, it looks like this is the only ice bet you lost.Robert Grumbinehttps://www.blogger.com/profile/10783453972811796911noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-59616028762502036492009-10-05T14:35:46.760-04:002009-10-05T14:35:46.760-04:00Now it is October. I could dig up the data but I b...Now it is October. I could dig up the data but I bet you have it.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-53572797632279437382009-10-01T09:13:23.224-04:002009-10-01T09:13:23.224-04:00"it's tough to make predictions, especial..."it's tough to make predictions, especially about the future."<br />- Yogi BerraBayesian Bouffant, FCDnoreply@blogger.comtag:blogger.com,1999:blog-5337555368793819627.post-75958140298742183222009-09-30T17:26:57.973-04:002009-09-30T17:26:57.973-04:00Why does the observed September average (in blue) ...Why does the observed September average (in blue) have a distribution (i.e. a standard deviation)? Given that the observed average is just one value (5.25), shouldn't it be just a vertical bar?<br /><br />I think that we have about 30 years of satellite monitoring of sea ice. Why do you use the average of the <b>first</b> 15 years of the satellite era (or previous) to set the climatology? Given the melting trend since the beginning of the monitoring, it seems rather difficult that the ice pack jumps back to its state 30 years ago. Wouldn't it be more logical to take the <b>last</b> 15 years or the average of the whole satellite era as the climatology?<br /><br />Thanks!Jesús R.https://www.blogger.com/profile/08623637876422608968noreply@blogger.com