No CWD in Maryland or Missouri...yet
According to a press report by the Maryland DNR there are no signs of CWD among 872 free-ranging deer in the state. The sampling regime was intensive:
"The state’s current sampling effort was designed such that if 1 percent of the deer in either population had CWD, there is a 98 percent chance the disease would be detected."
That maybe a high prevalence for a recently introduced disease (let Damien fight me this one) but it is still a reasonable starting point.Maryland has been monitoring CWD since 2002 and has passed legislation prohibiting the transportation of deer across state lines (the most likely cause of the appearance of CWD in NY and probably WI). Good going!
Spending tons more money, Missouri has also been cleared of the disease this year (10,352 sample from 52 counties!!). Somebody should teach them something about sampling!!
ahumadameister.
posted by Anonymous @ 6:05 PM
1 comments
1 Comments:
It's important to remember what these percentages mean. I don't know how many deer are in Maryland, but given that 75,000 deer were shot I would bet there are more than 500,000. Their sampling scheme was designed to detect a prevalence of 1%.
Sampling 872 deer gives you a 99% probability of detecting 1 positive deer in a population with 0.5% prevalence, or in this case 2625 deer (if we assume there are 500,000 deer there). In other words, there could still be over 2000 CWD-positive deer in Maryland, undetectable by this sampling strategy.
Note: To calculate this, I used the "rule of 4.6" approximation (4.6 divided by your sample size approximates the probability of detecting at least one positive in a population with 1% prevalence), and assumed sampling was totally random (which is unlikely).
I think Missouri is on the right track, although I'm not sure from the article if there are counties that aren't going to be sampled.
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