HITs Takes a Hit… Maybe

Solid research is produced over a long period of time with validation and verification of standards.  When using tools there must be a set of numbers that validate what data is being collected – in short to make sure the data is “good”.  This has been a problem with many things in the concussion realm, most notably with computerized concussion testing.  However last night I received an email with an abstract regarding the Head Impact Telemetry system or HITs.

Before we go further you will need to familiarize yourself with a couple of statistical terms: absolute error and root-mean square error.

Absolute Error is the amount of physical error in a measurement, period.  The example I found was when using a ruler on the metric side the absolute error of that device is +/- 1mm.

Root-Mean Square Error is a frequently used measure of the differences between values predicted by a model or an estimator and the values actually observed.  This measure is used to compile the deflection of errors in predictions and is good summation of accuracy, which only holds true for a particular variable not between variables.  In other words RMSE shows us how accurate the data is compared to its model/validation.  If this number is high it can show that either the model was incorrect or that the data was compiled incorrectly.

Appearing in the online version of the Journal of Biomechanics researchers from Wayne State (one of the notable places for head impact testing) found that a difference in helmet size on the Hybrid III head model has called into question the validity of the HIT system (abstract);

On-field measurement of head impacts has relied on the Head Impact Telemetry (HIT) System, which uses helmet mounted accelerometers to determine linear and angular head accelerations. HIT is used in youth and collegiate football to assess the frequency and severity of helmet impacts. This paper evaluates the accuracy of HIT for individual head impacts. Most HIT validations used a medium helmet on a Hybrid III head. However, the appropriate helmet is large based on the Hybrid III head circumference (58 cm) and manufacturer’s fitting instructions. An instrumented skull cap was used to measure the pressure between the head of football players (n=63) and their helmet. The average pressure with a large helmet on the Hybrid III was comparable to the average pressure from helmets used by players. A medium helmet on Continue reading

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