Assateague Sex Ratio Still Favors Mares

NPS said there were 22 males (29.3%) and 53 females (70.7%) on the Maryland side of the island in November, according to a story posted today by WMDT News of Salisbury.

The observed sex ratio of a wild horse herd will rarely be 50/50, but how far must it deviate from that value to indicate problems?

The answer must be found by calculation, using basic statistical formulas, where p-bar = .5 and n = 75.  The range of variation between males and females attributable to natural causes is therefore .327 (32.7%) to .673 (67.3%).

Assateague Census Nov 2019-1

The observed proportions fall outside those limits, so an explanation should be sought.

If the observed proportions fell inside the limits, there would be no clear indication of trouble and an investigation would be a waste of time.  The herd would be treated as if its sex ratio was 50/50, even though the observed value was, say, 38/62.

RELATED: Latest Assateague Census Shows No Improvement.

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