Tuesday, November 17, 2009

Motorcycle Crash Causation Study and the crash sample 900

As the Motorcycle Crash Causation Study folks have decided to do the study with 300 instead of 900 crashes sampled, time to review previous statements from study stakeholders on the matter. 

This story from Examiner.com from last week reveals that Dr Ahmed, the study Principal Investigator, is now working on some statistics to prove that the 300 number will be OK.  (We can confirm the Examiner story from our own sources)  This is ludicrous on the face of it.  The workings of the 'chi-squared' test make it impossible to predict which data will be further studied to see which of the almost 2000 crash data items are important in causing -and preventing - crashes.  These might be items like ABS, running lights, HID headlights, which might prove effective in preventing crashes if present in sufficient numbers in the population sample.   As we don't know what these numbers will be, we can't predict the outcome of the 'chi-squared' test done on these data at the 300 and at the 900 level.   No statistical calculations can override this presumption.

On the other hand, Dr Ahmed, the Principal Investigator from OSU,  is on record, in this LA Times article from July 2007, by the prescient Susan Carpenter, as saying "900 is the least we consider adequate from a statistical point of view.".   Right on, Dr. A, you were right first time.

 
This Pooled Fund solicitation, from Carol Tan, the FHWA Project Leader, is similarly firm on the subject, and in fact has a contract with the six state motorcycle administrators from New York, Ohio, Oklahoma, Rhode Island, Texas and Wisconsin.   

Not to mention the Transportation Committee could reasonably have expected that they were approving 900 crashes when they approved SAFETEA-LU measure 5511, if they were going by the published information on the subject. 


And, for good measure, we include other 900 supporters who are safety experts, including MSF, the Hurt and Maids studies, Motorcycle Safety News and Safety Net.   


The good news is that study petitions have gone viral and are coming in  too fast to count.  We are well on the way to 1000 petitions, and have been getting them from organizations like AMA, SCRC, Blue Knights, ABATE members from several states, Christian Motorcyclist Assoc and many more.  Thank you all for your support, and we are still investigating the issue.  





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