will generally maintain one or more Autonomous Systems, bearing the responsibility to maintain announcements and peering, for the connectivity leased to other smaller ISPs, government agencies, educational institutions or commercial organizations. Additionally, since traffic paths across networks are constructed using centrally allocated components of ASNs and address prefixes, both are registered and externally queriable.

Control Groups:

:   We attempt to identify logical, coherent groups of networks and clients based on common characteristics, such as the nature of the end user or performance. Control group measurements differ from service providers because they are defined as narrowly as the data allows, rather than existing segmentations. Such groups, particularly when defined by network degradation, are possibly deterministic, however, these often produce surprising and mixed results, as described in Section \[sec:findings\]. Furthermore, the grouping of networks or entities, such as state agencies or educational institutions, during one incident is testable under other circumstances and may serve as a control for future monitoring.

Finally, detection of significant events generally follows one of two themes. These mechanisms are designed to highlight precipitous changes of service quality as a warning system to flag potential events, however, they are not the holistic determinant of interest.

Threshold:

:   A 