Again, the Key Category analysis is primarily useful to help you prioritize your review work. However, some checks should be made (probably by the generalists on your team) to be sure that each Party has prepared a rigorous key category analysis.

The first item you should check is obviously whether the Party has prepared its own Key Category analysis. As long as the Party has submitted a reasonably complete set of CRF tables, the UNFCCC Secretariat will have prepared a Tier 1 Key Category analysis for your use, which is included in the review transcript. Parties should have also completed their own.

It may be useful to quickly compare the Party’s own analysis with the analysis prepared by the UNFCCC Secretariat (e.g., for your Sector). Although it is completely acceptable for a Party’s own key source analysis to differ from the one prepared by the Secretariat, any differences should be due to special considerations the Party has identified and explained within its documentation.

In all cases, the Party must use the level and trend criteria for identifying its Key Categories.  They should also consider qualitative criteria. Table 7 in the CRF tables includes useful information on a Party's Key Categories. More detailed information should also be provided in the Party’s National Inventory Report (NIR).
When Parties identify their key categories using a trend analysis, they should use the base year under the UNFCCC (i.e., 1990 or other year for some EIT Parties).  Although some Parties may use 1995 as a base year for accounting their assigned amounts from HFC, PFC, and SF₆ emissions under the Kyoto Protocol, it should not be used as the base year for the key category analysis.

Based on your own expert judgment, though, you should evaluate the identification of Key Categories as to its “reasonableness.” The inclusion or exclusion of particular source or sink categories from the list of Key Categories should be representative of national circumstances.

For example, a source or sink category cannot be identified as key if it is missing from a Party’s inventory in the first place (i.e., no estimate is provided). Therefore, failure to provide an estimate for a large category does not mean it is not a key category. In other words, if you blindly focus only on Key Categories, you could potentially miss important omissions in a Party’s inventory.

Finally, if the Party has identified its Key Categories using a Tier 2 method (incorporating quantified uncertainties), then it should be reviewed in conjunction with the Party’s Uncertainty analysis.

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