Regal’s Civilization Termination Index
Regal's Civilization Termination Index (RCTI) is a standardized reference for indicating which of the many typical ways subluminal civilizations come to an end.
The RCTI is divided up into major categories, and from there into various subcategories. While there are many CTIs, Regal's is the most widely accepted because of its simplicity and mutability. It may not always be useful or helpful, but it is always easy to use.
The categories are, roughly summarized:
1: Astronomical. A species destroyed by any off-world event falls into this category.
2: Planetary. Not all homeworlds or ecologies are stable. But this only includes natural disasters.
3: Personal. Whether this is nuclear war, climate change, temporal erasure, or genetically engineered squid monsters, this is the category for all the civilizations that self-destruct.
4: Foreign Interference. When another species causes the downfall, either on purpose or on accident.
5: Other. Example: Vayl Millauk.
The RCTI is referenced extensively by the Watchers Council when debating on whether to initiate Measures for Sapience Recovery, and the Karvassian Buoys contain explanations for each, as well as advice on how to avoid them... for those capable of understanding the buoy's notoriously difficult language.
But it is far from the only means of categorizing the last days of a civilization. Other indices often focus on a specific attribute useful for the kind of analysis in question.
For example, Alphaspace Watch uses the DCTI, which categorizes downfalls by how they are likely to impact and attract foreign travelers, while Youth Helpers prefer the PCTI, which focuses on analyzing preconditions to prevent downfalls.