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[RC] Horse rider weight reply part 1 - Sisu West Ranch

Susan:

I am sorry if I appeared to be slamming your peer reviewed article. I certainly will read it and comment if appropriate, but this will probably not happen until next winter, there are to many outside things going on right now.

Please let me try to explain some of my feelings about studies, journal articles, and correlation effects where controlled, confirmatory experiments either can not or have not been done.

First, I expect that I will find that the article will carefully define the population that was used in the study. This (unless I am really off base) will be those who chose to enter Tevis one particular year. Later in the article there will most likely be a paragraph explaining how the conclusions may not apply to other groups.

The discussion on Ridecamp was about generalizing this study to all endurance horses and riders and some posters started talking about how really big Arabian horses are most likely less sound than ordinary Arabian horses. Immediately we do not know that the larger horses, who obviously were those entered in the ride, were large Arabian horses.

My background relates mechanical/chemical engineering and the manufacturing of products for sale. We often had to start studying a problem by attempting to correlate properties of the final product with inputs. This is similar to what you were able to do at Tevis. While we never had the time and/or money to do enough experiments to track down all of the root causes we did have the ability to do some experiments to further understand the system. The eventual results of these experiments are what has led to my skepticism about the extrapolation of a correlation study to either cause and effect or to application to more that the original population. This is not a slam at the scientific quality of the original study, it is just a realization that things are not always as they seem

It is not uncommon in an initial study for an important variable not to be even considered. I have scaled up products to production where one of the important variables was not even considered until after 3 or 4 months of inconsistent production.

The classic one I ran into early in my working life was the effect of room humidity on the quality of magnetic video recording tape. A large number of very smart people had been working for a number of years trying to figure out why sometimes the quality was better than at other times. At an informal meeting over coffee someone said "Maybe it is the phase of the moon". After the laughter died down, the group decided to plot the day of the year when good and bad product had been produced. It turned out that late summer and winter in the Midwest were both times when bad product was more likely to be produced. It turned out that either to much or to little water in the grind would produce "bad" product. As soon as this was understood it was possible to fix the problem.

Another thing I noticed is that when a sample is relatively small, it is possible for the statistics to say something is significant when it really is not significant. I have had conversations with industrial statisticians about this and have never received a good explanation, but I do know it is true. A correlation study or even experiment can say that at a 95% confidence level a coefficient is significant. Usually these coefficients are relatively small (that is they are responsible for say less than 25% of the observed variation), but statistically significant. Being a stubborn person, and having the luxury of dealing with non biological systems, I often would do further experiments which would not show the effect. If I was smart, or more often lucky, I would also have decided to measure and control a new variable which turned out to shed a lot of light on the process. I also noticed that these statistically significant, but ultimately misleading results were often in interaction terms. The total weight of the horse and rider team is that type of interaction term. Again I do not know why, but that is what I have observed

To be continued....



Ed

Ed & Wendy Hauser
2994 Mittower Road
Victor, MT 59875

(406) 642-9640

ranch(at)sisuwest(dot)us



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