Does tracking frequency of access find shared accounts?

No. At least not very accurately. Some online services have tried to use high frequency of access as a positive indicator of account sharing. The following example illustrates the limitations of that metric.

Scout Analytics has been analyzing access patterns for one online service that has approximately 6,000 active users. A recent regression analysis was performed where the percentage of shared accounts was correlated to the frequency of access as measured in standard deviations from the median. The graph below shows that frequency of access was not a good indicator until more than 9 standard deviations above the median which represented < 1% of the shared accounts.