For data on arrivals, the numbers we generate are for when we first
notice the species. Those of us who work during the day may miss a
genuine first arrival. Therefore, we should be loading our numbers
with qualifiers. Mean, median, standard deviation and maximum and
minimum all contain information that qualifies the statistic and each
by itself implies something different about arrivals.

With hummingbirds, where site fidelity is fairly strong, it is very
likely that if a bird shows up on multiple years on Feb 21, it may well
be the same bird (I had arrival dates in 4 consequetive years on Feb 21
and I put out the feeder on Feb 1). Site fidelity is as likely to
affect the mean arrival date more than say... El Nino.


>
>Or you could look at the mean and standard deviation (a measure of
>the distribution around the mean). One of the problems of trying
>to represent complex events by one or two numbers in order to make
>things manageable is that part of the story gets left out. In
>these cases you have to decide if this is an important part of the
>story or not.
>
>Ed Schulz
>email: eschulz at gte.net
>Phone: (425) 259-6877
>Everett, WA
>
>----------
>>
>> On Mon, 2 Feb 1998, Michael Price wrote:
>>
>> > But this is something I've never quite figured out how to deal
>with: data
>> > that are waayyy out of pattern: do you include them knowing
>they're likely a
>> > one-off that's gonna distort whatever means and averages, or do
>you ignore
>> > them? For example, let's say arbitrarily that this is the
>pattern of Barn
>> > Swallow arrival, leading to the derived (and equally arbitrary
>for purposes
>> > of this immediate discussion) average arrival date of April 07
>above:
>> >
>> > 4 12
>> > ----|----|----|----|----|----|----|----|----|----|----|----
>> > J F M A M J J A S O N D
>> >
>> > then along comes 1998, which leaves the record looking like
>this:
>> >
>> >
>> > 1 4 12
>> > ----|----|----|----|----|----|----|----|----|----|----|----
>> > J F M A M J J A S O N D
>> >
>> > which then pulls the average arrival date sometime into
>mid-March or even
>> > late February, clearly not reflecting reality. I'm sure there's
>something
>> > simple way to absorb that kind of temporary distortion of the
>'normal'
>> > pattern that I'm overlooking here. Anybody with statistics in
>their blood
>> > (ie, related to that famous Gaul, Vitalstatistix '-) who knows
>how to fix this?
>> >
>> > Michael Price A brave world, Sir,
>> > Vancouver BC Canada full of religion, knavery and
>change;
>> > mprice at mindlink.net we shall shortly see better
>days.
>> > Aphra Behn
>(1640-1689)
>> >
>> >
>>
>
>

--
*********************************
* Mike Patterson, Astoria, OR *
* mpatters at orednet.org *
http://www.pacifier.com/~mpatters