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Message: <blockquote data-quote="Mysticete" data-source="post: 3586995" data-attributes="member: 67784">I wonder if the best measure might simply be to determine the percentage of birds seen during the big year as a ratio of what was reported. That data would probably be harder to generate, but should factor out taxonomic changes and countability changes, while also providing a correction factor for year to year differences in number of vagrants reported. Some years are just plain better and have larger number of vagrants show up, and presumably there is also an observer bias, with vagrants probably getting reported and identified at higher rates than they would have decades ago.Still won't completely even things out, but I suspect it might work better than a pure percentage of the list or the "x-factor"</blockquote>