[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

*To*: "'Philidor11@aol.com'" <Philidor11@aol.com>, jjackson@interalpha.co.uk*Subject*: RE: EARLY EVOLUTION OF 'BIRDS'*From*: "Stewart, Dwight" <Dwight.Stewart@VLSI.com>*Date*: Fri, 6 Nov 1998 16:19:34 -0800*Cc*: dinosaur@usc.edu*Reply-to*: Dwight.Stewart@VLSI.com*Sender*: owner-dinosaur@usc.edu

-----Original Message----- From: Philidor11@aol.com [SMTP:Philidor11@aol.com] Sent: Friday, November 06, 1998 3:25 PM To: jjackson@interalpha.co.uk Cc: dinosaur@usc.edu Subject: Re: EARLY EVOLUTION OF 'BIRDS' In a message dated 11/6/98 12:19:53 PM Eastern Standard Time, jjackson@interalpha.co.uk writes: > I'm following your argument slowly. The Law of Averages, or regression to the mean, says that if you start flipping a coin and heads come out 9 times in a row, and then you keep flipping thru the eons, sometime before the sun burns out or blows up or both you will probably have 9 more tails than heads. But don't count on it. The idea that 9 heads in a row affects the next flip is called 'Gambler's Fallacy' and is a major money maker. The kind of meta-analysis you're talking about was recently used by Shafer et al at Harvard to look at 20 years, give or take, of pathological gambling prevalence studies. He observes the inadequacies of each approach used, then tries to combine them to draw a conclusion that pathological gambling has increased in recent years. His reasoning is that because some inadequate studies before a certain date he picked produced some results just outside the high end of the range of the inadequate studies after that date, therefore pathological gambling has increased. The difference in ranges is in the hundredths of a percent. More relevantly, your mickles had better had some validity to begin with. I don't think inadequate results gain strength in numbers. Validity in this case refers to the likelihood that a fossil will be discovered. You're assuming both that each of the creatures you're comparing were equally likely to fossilize and that the places where they were discovered were a representative sample of the large area you're concerned with. Hi, All; Here's the 'short n' sweet' of the ole coin toss: Each time you toss the coin (IF there are no limiting factors, such as cheating somehow) there is a 50/50 chance that it will land heads up or tails up. Previous tosses & future tosses have no bearing on the outcome. There is a mathematical tendency to approach a mean state. That is, as Brian states; if you toss your coin over a long enough period of time, the rate of occurrence will be APPROXIMATELY 50%. BUT - how does one define the length of time needed to approach the mean state. With a coin toss, about 20 tosses should do it. All things being equal, 9 heads or tails in a row CAN occur, but will be rare. Sampling is the issue & with fossilization it seems that sampling is skewed automatically. For example: dinosaur fossils preserved from what were mountainous environments are rare. This doesn't mean that some dinosaurs weren't as adept at mountainous living as modern day goats. It MIGHT mean that, but it might equally mean that the conditions for preservation are less conducive from mountainous regions. This might be a poor example, but the point is that statistics can be very skewed or even rendered inaccurate by sampling. This is complicated by interstitual or matrix inbedded chaos. No matter how ordered a system is, there is always an element of chaos inbedded within the structure. The reverse is also true. In a complex system, which all biological sytems are, there are numerous Elements of chaos (or unpredictability) within the structure. One element would be variation in animal behavior. The point being that a sampling population could seen intuitively robust, but in fact be seriously skewed to produce one outcome or another. Dwight

- Prev by Date:
**BIRDY _ARCHAEOPTERYX_** - Next by Date:
**Re: Polly Want a Dinosaur?** - Previous by thread:
**Re: EARLY EVOLUTION OF 'BIRDS'** - Next by thread:
**Re: EARLY EVOLUTION OF 'BIRDS'** - Indexes: