CBC Compilers: The High Count (HC) flag

You should flag a species as high-count if its numbers are more than two standard deviations above the mean. For example, if the mean count for a species is 50 and the standard deviation is 60, you should flag as HC any records greater than 170 (that is, 50 + 60*2).

There are two exceptions to this general rule:

• Some lines in the table are affected by species splits or lumps. For example, Red-naped Sapsucker was split from Yellow-bellied Sapsucker in the 1980s, so all older records will show as the latter species. In such cases, the mean and standard deviation are not correctly computed. Use your own judgement.
• If the numbers are up due to increased coverage (more observers, or observers who work parts of the circle not usually covered), you need not flag the record as high-count even though it passes the statistical test.

In general, your judgement should take precedence over blind obedience to the statistical rule. If you feel that a given species has not increased despite increases in observed numbers, don't flag it. Conversely, if you think a species is significantly more numerous in the current year, flag it as HC even if it doesn't pass the test.

Last updated: 2000/05/04 18:20:24
URL: http://www.nmt.edu/~shipman/z/cbc/hc_flag.html