From Fri Feb 23 13:47:09 1996

Subject: More Random

[Note: this is a response to "christine bishop" <>: Fri, 23 Feb 1996 10:03:36 -0600 (CST)]

Someone from LPBO wrote: "So our methods are not as rigorous statistically in terms of choosing the locations of the survey routes as has been suggested is necessary. But I think they are providing very useful information which is standardized over time, a lot better than anything in the past."

Careful! Collecting things for a long time doesn't heal statistical deficits. In some cases it comes out in the wash, but in many instances the biases are such that they can completely disguise long as well as short-term population trends.

LPBO: "The value of the information might be even better if the routes were more random and more stratified. On the other hand, I have discussed this with several statisticians and all but one says that our approach is statistically valid and does not need to change."

It all depends on your goal. If your goal is to track trends you need to use random surveys, if you have other goals (e.g., educational, phenology) then maybe you don't. However, if you want to make statistically defensible statements about trends in amphibian populations in a region, then all statisticians will agree that you cannot use observer chosen sampling programs without biasing the results. This was hammered out in the 20's and again in the game biology field in the 50's, at great loss of information. The earlier years of observer chosen wildlife surveys for waterfowl and upland game birds have all had to be dropped from the long-term data sets. They could not be corrected for and effectively those groups lost many years of information on population trends and had to start completely over. Please, please, please, don't lets make the mistakes of the past. That ancient but relevant literature is reviewed in Appendix 1 of the AMP document ().

In calling surveys, a system of observer-chosen routes can oversample regions near population centers and observer homes. Thus trends will reflect trends in regions near people rather than the population of amphibians as a whole. A suburban bias will likely develop.

Observers also tend to choose "nice" protected sites already with lots of calling amphibians to do their surveys. In this case observers have built negative declines into the system because these sites, now at their zenith are more likely to decline than increase.

LPBO: "At present we have a decent coverage of southern Ontario but only 5 or so people in northern Ontario. We want more volunteers in central and northern Ontario and we are not going to discourage volunteers if they can't do a survey route we assign to them but can do something closer to home. Assigned routes are ultimately a nice goal but data collected other wise, I believe, has value."

The best compromise here is to do both. Have random routes as the priority within the monitoring system. These would be assigned prior to letting non-random routes be formed in an area. Non-random routes are great for education, engaging the public, tracking phenology, training, and citizen projects, but it should be made clear to participants that running the priority random routes are the main objective and contribute the most to tracking population trends.

In the end the random routes will provide us with tremendous power to track and publish information about population trends.


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Sam. Droege FROG@NBS.GOV

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The Kingbird

Kill not thy friend, who thy whole harvest shields,

And sweeps ten thousand vermin from the fields;

Think how this dauntless bird, thy poultry's guard,

Drove every hawk and eagle from thy yard;

Watched round thy cattle as they fed, and slew

The hungry, blackening swarms that round them flew,

Some small return - some little right resign

And spare his life whose services are thine!

-Alexander Wilson