From: sommar@enea.se (Erland Sommarskog)
Subject: UAP #28 - Peter Gabriel, reminder
Followup-To: poster
Keywords: Usenet Artists Polls
Organization: Enea Data AB
Date: Sun, 24 Jan 1993 21:11:35 GMT

As I've announced in a seperate article, Peter Gabriel will be the
third-to-last Usenet Artist Poll, followed by Genesis and Roxy Music.

Deadline is January 30th.

Below is a discography of Peter Garbriel's solo albums. Please feel
free to enter any item I've forgot to include, but as always please
no bootlegs, videos and interview albums.

Please, use the discography as a template for your ballot. Particularly
observe how I'm referring to his four first unnamed albums. (The fourth
album was called "Security" only in the US.) I've included one song from
each as a comment if you don't know which is which. I've also included 
the German versions of the 3rd and 4th albums, although they are very close
to the original albums.


&BEGIN
Peter Gabriel                                <Solsbury Hill>
Peter Gabriel (2)                            <On The Air>
Peter Gabriel (3)                            <Intruder>
Ein Deutsches Album (3)
Peter Gabriel (4)                            <Shock the Monkey>
Ein Deutsches Album (4)
Peter Gabriel Plays Live
Birdy
So
Passion
Shaking the Tree
Us
&END

If you are new to these polls, please read the instructions below.
If you interested in reading about the algorithm I use to compute
the results, there is a descpription following the instructions.

How to vote
-----------

Use the list above as a template for your ballot. Sort the list
so that your favourite comes right after the &BEGIN and your
least favourite just before the &END. Delete albums you are not
familliar with. One album by line. No numbering. Please delete
quote characters like ">" from your ballot.

If you can't tell two or more albums apart you can declare a
tie. You do this by preceding the albums with &TIE. The tie
lasts until the next &END. The number of &END on the ballot
must be equal to the number of &TIE + one for the &BEGIN.

If you feel that there is a big gap between two albums you
can mark this with a filler. A filler has the format &FILLERn
where n is a positive number, default is 1. Notice that a very
big value of n make little sense; the net effect is the same
declaring an &TIE on the albums separated by the &FILLER.

To participate you need to know at least two albums, so you don't
have to be shy. Ballots are weighted, so the more you albums you
know, the more influence do your ballot get.

For further details on the algoritm, see below if you are interested.

*MAIL* your vote ballot to me, sommar@enea.se. I try to acknowledge
all votes, so if you do not receive an ack after a few days, please
mail me again.

If your mailer leave a decent return address *and* your ballot mail
has a non-empty subject line, you will get the results in your mailbox.
If you want the results to another address, please state so, but no
guarantees.

You are welcome to send in a vote for a friend who does not have net
access. Just indicate that the vote is for someone else so I know that 
it's not a duplicate.

Have fun!

The Algorithm
-------------

This an example ballot for an imagninary group: (The numbers in the
right are NOT part of the ballot as you write it, but are used for
the description below.)

&BEGIN
She Comes in the Morning                      0.5
Next Day                                      0.4
&TIE
Looks Like Trouble                            0.25
Futuralized                                   0.25
&END
On the Way Down                               0.1
Cram it!                                      0.0
&FILLER4
Last Really Crappy Album                     -0.500
&END

The algorithm to compile the results of a polls consists of a
number of steps.

Step 1:
For each individual ballot, the intervall from -0.5 to 0.5 is sliced
up at (N + F + 1) equidistant points, where N = number of entries,
and F = number of fillers. In the example ballot N = 6 and F = 4.
The top album gets 0.5 points, next album ((N+F) / (N+F+1)) - 0.5
points, third best gets ((N+F-1) / (N+F+1)) - 0.5 points etc, down 
the last which gets -0.5 points. If two or more albums are tied,
they get the average of the involved points. The net result for
the example ballot is illustrated by the number on the right side.
(Side note: if we forget the fillers, the method corresponds to the 
one you use for pairs competitions in bridge.)

Step 2:
In order to avoid distortion from voters who only know the 2-3
most popular albums, the ballot is weighed so that the points 
from step 1 are multiplied with sqrt(N).

Step 3:
All ballots are added together and for each album we get a number
of points P = ((p1 + p2 ... pM) * 1000 / M) * C + 500, where M = 
the number of ballots the album appears on, and C is a poll constant.
Thus, the result for an album is indepentent on how well-known it is,
However there is a cut-off rule, so albums which only appears on one
or two ballots are excluded from the final result.

The Poll Constant:
This constant is sqrt(B/T) where B where B is the number of ballots 
in the poll and T is the total number of entries on these ballots.
The idea with the poll constant is to remove the effect of the weighing
factor from the range of the points, so we can compare polls with
each other. If an album tops all ballots, it will get 1000 and 0 if
it is ranked last by all voters. Note however that this compensation
is a rough model. If an album tops five ballots of ten, and is not
mentioned on the other five, its result can be bother higher and 
lower than 1000 depending on the weight of these ballots.
-- 
Erland Sommarskog - ENEA Data, Stockholm - sommar@enea.se
Newsgroups: rec.music.misc