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The table below shows summary data for each device. The count field is how many measurements I have for that combination of condition and device, with each measurement being a quarter mile distance. I generally aim for over 1,000 data points to even out the effects of weather, satellite position and other factors. The Trueness is the absolute of the mean, though nearly all watches tend to read short. The standard deviation is provided based on the variance from the mean and the variance from the known true value. The average pace error is shown to give a sense of how much error you're likely to see in the display of current pace. This is an average error not a worst case. The data shown below is a summary the accuracy based on all the sections. If you'd like more detailed information, I've split off the [[Detailed Statistics for GPS Running Watches]] for the results under different conditions.
{{:GPS Accuracy-statistics}}
The "Accuracy (Combined)" column has an indication of statistical significance compared with the most accurate entry. The key to this indication is: † p<0.05, * p< 0.01, ** p< 0.001, *** p< 0.0001, **** p< 0.00001, ***** p< 0.000001
==Progress of newer watches==
I expected GPS watches to improve with time, but the opposite appears to be happening. With the Garmin devices especially, you can see that the older watches generally do far better than the newer ones. I suspect this is due to compromises to get better battery life and smaller packaging and the cost of GPS accuracy.
==Smartphone Accuracy==
There are various things you will need to do in order to get the level of accuracy I found with Smartphones. See [[Running With A Smartphone#Optimizing GPS Accuracy| Optimizing Smartphone GPS Accuracy]] for details.
==Interpretation and Conclusions==
What do these statistics mean? This is my interpretation:
