reid@decwrl.dec.com (Brian Reid) (06/01/87)
USENET READERSHIP SUMMARY REPORT for May 87
This is the first article in a monthly posting series from the Network
Measurement Project at the DEC Western Research Laboratory in Palo Alto,
California.
This survey is based on a sample of data taken from various USENET sites.
At the end of this message there is a short explanation of the measurement
techniques and the meaning of the various statistics. The messages that
follow this one show survey data sorted by various criteria.
The newsgroup volume and article counts that I post are often significantly
different from the ones posted by Rick Adams, because he includes the size of
a crossposted article in every group to which it is posted, whereas I charge
that size only to the first-named group.
The complete set of readership data (of which this is a summary) is posted
in news.lists. The software that will let your site participate in the
survey is in comp.sources.d and news.admin
Brian Reid
OVERALL SUMMARY:
This Estimated
Sample for entire net
Sites: 477 6800
Fraction reporting: 7.01% 100%
Users with accounts: 71247 1015000
Netreaders: 14297 203000
Average readers per site: 30
Percent of users who are netreaders: 20.07%
Average traffic per day (megabytes): 1.977
Average traffic per day (messages): 957
Traffic measurement interval: last 21 days
Readership measurement interval: last 75 days
Sites used to measure propagation: 320
Valid data received from these sites:
1141g 3comvax 4gl aaec abel abstl abvax.abnet.com acetes acornrc adelie
akov68.dec.com alberta alliant alv amdahl amdcad ames
amsterdam.columbia.edu ant.dec.com argus arran.tcom.stc.co.uk
arthur.cs.purdue.edu ascvax astroatc astrovax atari athena atssc aurora
ausmelb auspyr axis babbage banana.cs.uq.oz bandit.dec.com basser
bcm5000 bdmrrr bellman beno beowulf.ucsd.edu binkly.dec.com bms-at bnl
boole boris brand briar.philips.com brillig brspyr1 btnix bu-cs bucasb
bucket bucsb.bu.edu bucsd buengc buit1.bu.edu burl bute.tcom.stc.co.uk
cacilj cad.dec.com cadomin caip.rutgers.edu calgary cascade
casee.dec.com catsim cavell cbosgd cbterra cca cfisun cgcha
cgfsv1.dec.com cgl.ucsf.edu cgou01.dec.com chalmers chaos charlie chas2
chinet ci-dandelion cideq3 circe cisunx cit-vax cit-vlsi clinet clio
clt.dec.com cognos concurrent.co.uk cortex cos cpro cpw.columbia.edu
crcge1 crin crvax1.dec.com cs.nott.ac.uk csadfa csm9a csustan
curium.dec.com cuuxb cvl cwruecmp cxsea dalcs dale dalton darth dasys1
davaar.tcom.stc.co.uk davasun dayton dciem dcl-cs decsim.dec.com
decwet.dec.com decwrl delni.dec.com desint devlab.dec.com devon dgis
dhw68k diamond.bbn.com diehrd.dec.com dinadan dlb dukempd dvlmarv dycom
earvax ecsvax ector.cs.purdue.edu edison elbereth.rutgers.edu elrond
elroy elsie ems endor enea eneevax eneevax.umd.edu eplunix
ernie.berkeley.edu eros esc-bb eta ethos euler.berkeley.edu euraiv1
exodus.dec.com fai fedeva felix firqb.dec.com fortune furilo.dec.com
garfield gatech geac genrad geocub gitpyr glacier grebyn grumpy
gt-stratus gymble haddock.isc.com hammer hanyang hao harvisr hechcx
hefty.dec.com hi hjuxa hoptoad hpcea hpscad.dec.com hqda-ai hscfvax
husc2 husc4 husc8 hvrunix iapetus.rice.edu ichaya ico ileaf ima imagen
imt3b2 indian.dec.com infinet intrin iscuva ishtar isl islabs
istg.dec.com izimbra.css.gov jasper ji.berkeley.edu jimi.cs.unlv.edu
jplgodo kallon.dec.com killer kirk.dec.com kodak kolvi koning.dec.com
korppi labrea leah leia lemon.berkeley.edu lily lindy lion litp liuida
lll-crg lotus lzaz macbeth maccs mapper mas1 masscomp maxwell maynard
mcdchg mcgill-vision mck-csc me-ncr meccsd meccts mejac mendel mimsy
mind minnow mirror mit-eddie mks mnetor mntgfx mordred.cs.purdue.edu
moscom mss mstar msudoc mtgzz mtunb mtund mtune mtunf mtung mtunh mtuni
mtunl mulga munnari munsell myrias naakka nac.dec.com navajo nbifet
nbires ncoast ncr-sd ncrcae nears noao novavax nttlab oberon oblio
ocean oddjob.uchicago.edu olivea olivee olivej oliven omepd onecom opus
orca orchid orion.arpa osiris osupyr oulu panda pbhya pbhyb pbhyc pbhyd
pbhye pdn pdnbah pegasus percival phoenix phoenix.princeton.edu phri
piaget pixar plaid plus5 pluto pogo popeye popvax poseidon princeton
psivax ptsfa pwcs pyramid pyrnova pyrps5 qiclab qtc quad1 quoin.dec.com
ra rainbo.dec.com rayssd rayssdb rayssde remsit renko.dec.com
renoir.berkeley.edu retix rhea.dec.com ritcv rlpyr-a rlvc rlvd
rochester rocky rose rosevax rsts32.dec.com ruby sandoz saturn sauron
scgvaxd scicom sdcsvax sdn se-sd shark shasta sibelius sics sicsten
sigma soma sphinx spock sqm.dec.com sri-spam star.dec.com stb stl styx
suadb sunybcs svo tahoe.dec.com tallis.dec.com teddy tekecs teklds
tekred temvax tesla teti thelink tiger titan.rice.edu tmsoft
topaz.rutgers.edu tropix trwspf tucos turtlevax tutctl tutor twitch
tymix ub ubc-cs ubvax ucbarpa.berkeley.edu ugdist uhnix1 uhnix2 uiucuxa
uiucuxc uiucuxe uiucuxf ukecc ukma ulowell ultra.dec.com umd5.umd.edu
umnd-cs-gw uncle.dec.com unsvax.uucp uqcspe.oz ur-laser usc-oberon
utacs utrtsc.dec.com uwmacc van-bc vaxtrain vianet video.dec.com
viking.dec.com vilya violet.berkeley.edu viper virginia voder voodoo
vrdxhq vu-vlsi vulcan walldata wanginst ward watale watarts watcgl
watdaisy watdcsu watdragon wateng water watlion watmath watmum watnot
watopt watrose watsol watt watvlsi well wiley wmois.dec.com wnuxb wolf
wp3b01 wuphys xanth xios yarra yetti yogi.dec.com z.dec.com zaphod zeus
zorro
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EXPLANATION OF THE MEASUREMENTS AND STATISTICS
Survey data is taken by having one person at each site run a program called
"arbitron", which looks at the news or notes files and determines the
newsgroups that the user has read within a recent interval. To "read" a
newsgroup means to have been presented with the opportunity to look at at
least one message in it. Going through a newsgroup with the "n" key counts
as reading it. For a news site, "user X reads group Y" means that user X's
.newsrc file has marked at least one unexpired message in Y. If there is no
traffic in a newsgroup for the measurement period, then the survey will show
that nobody reads the group. For a notes site, "user X reads group Y" means
that user X has been in the notesfile with the sequencer in the last 14 days.
The "14 days" interval for notesfiles corresponds to "unexpired" for news.
The "arbitron" program is periodically posted to comp.sources.d, or is
available from me (decwrl!reid). The notesfiles version of the program should
be available through standard notesfiles software distribution channels as
well.
SITES SURVEYED IN THIS SAMPLE
"This Sample" means the set of sites that have sent in an arbitron report
within the past "Readership measurement interval" days. In every case the
most recent report from each site is used. At the moment, some of the
readership reports are several months old. In future postings those reports
will have expired and will not be included.
One might argue that the sample is self-selected, and thereby be biased. It
does in fact have a certain self-selection factor in it, because we only get
data from sites at which someone participates in the survey. However, we do
not require the participation of every user at a site, only one user. The
survey program returns data for every user on the system on which it was run.
Since there are an average of 30 people per site reading news, there is a
certain amount of randomness introduced that way. Of course, the sample is
biased in favor of large sites (they are more likely to have a user willing
to run the survey program) and software-development-oriented sites (more
likely to have a user *able* to run the survey program). I intend to post,
reasonably soon, some breakdowns of statistics about the sites that have
responded.
NETWORK SIZE
I determine the network size by looking at the set of sites that are
mentioned in the Path lines of news articles arriving at decwrl. This number
is consistently higher than the number of sites that posted a message (as
measured and posted from Seismo) because it includes passive sites that are
on the paths between posting sites and decwrl. Each month I store the names
of the hosts that are named that month, and for this report I used the past
13 months worth of data.
There are 6758 different sites in the Path lines of articles that
arrived at decwrl in the last 13 months. There are 3704
different sites in the comp.mail.maps data, but comp.mail.maps includes every
site that participates in uucp; there is a considerable number of machines
that exchange uucp mail but do not get USENET. Of those 6758 sites,
44 (0%) are DEC E-net hosts not part of uucp, and
which therefore are not included in the 3704 figure.
Despite these various difficulties, I believe that 6800 is the best
estimate for the size of USENET. Because it is actually a measurement of the
number of sites that have posted a message or that are on the path to a site
that has posted a message, it will be slightly smaller than the number of
sites that actually read netnews. Any site that believes it is not being
counted can just ensure that it posts at least one message a year, so that
it will be counted.
NUMBER OF USERS
The number of users at each site is determined in a site-specific fashion.
Sometimes it is done by counting the number of user accounts that have
shells and login directories. Sometimes it is done by counting the number of
people who have logged in to the machine in some interval. Sometimes other
techniques are used. This number is probably not very accurate--certainly
not more accurate than to within a factor of two.
ESTIMATED TOTAL NUMBER OF PEOPLE WHO READ THIS GROUP, WORLDWIDE
There are two sources of error in this number. The number is computed by
multiplying the number of people in the sample who actually read the group by
the ratio of estimated network size to sample size. The estimated total can
therefore be biased by errors in the network size estimate (see above) and
also by errors in the determination of whether or not someone reads a group.
Assuming that "reading a group" is roughly the same as "thumbing through a
magazine", in that you don't necessarily have to read anything, but you have
to browse through it and see what is there, then the measurement error will
come primarily from inability to locate .newsrc files, which can either be
protected or moved out of root directories. There is no way of measuring the
effect on the measurements from unlocated .newsrc files, but it is not likely
to be more than a few percent of the total news readers.
PROPAGATION: HOW MANY SITES RECEIVE THIS GROUP AT ALL
This number is the percent of the sites that are even receiving this
newsgroup. The information necessary to compute propagation was not generated
by early versions of the arbitron program, so the "basis" (number of sites)
used to generate the Propagation figure is smaller than the "Sites in this
sample" figure. A site's data will be used to compute propagation if either
(a) it reports zero readers for at least one group, or (b) it is using an
arbitron with an explicit version number that is high enough.
MESSAGES PER MONTH AND KILOBYTES PER MONTH
Traffic is measured at decwrl, in Palo Alto, California. Any message that has
arrived at decwrl within the last "Traffic measurement interval" days is
counted, regardless of when it was posted. Monthly rates are computed by
taking the total traffic, dividing by the number of days in the traffic
measurement interval, and multiplying by 30. Decwrl runs 2.10.3 news, which
does not store the "Date-Received", "Relay-version" or "Posting-version"
header lines; the amount of space occupied at your site might be higher, and
the number of bytes transmitted between machines is probably higher. By
definition this number is correct, because it is an exact measurement, but it
may differ from the traffic at your site by as much as 15% due to timing
differences and news version differences. Timing differences will be random,
but will average out in the long run. News version differences will cause a
systematic error that is additively uniform across all newsgroups, and which
therefore does not significantly affect ratios.
If a message is crossposted to several groups simultaneously, it is charged
only to the first-named group in the list.
PARTICIPATION RATIO: MESSAGES per MONTH per 1000 READERS
This number is exactly what it says: the number of messages per month in
that newsgroup, divided by the number of 1000 readers. It is an indication
of how involved the readers of the group are in the traffic, of whether they
are mostly listeners or mostly talkers. Its accuracy is limited by the
accuracy of its two components. The messages per month figure is exact; the
reader count is only as accurate as the network size estimate, which is in
worst case accurate to 40%. Therefore you should treat this number as having
an error margin of plus or minus 40%. However, ratios between participation
ratios for different newsgroups are quite accurate, since the network-size
component divides out.
COST RATIO: DOLLARS PER MONTH PER READER
The most controversial field in the survey report is the "$US per month per
reader". It is the estimated number of dollars that are being spent on
behalf of each reader, worldwide, on telephone costs to transmit this
newsgroup. The cost ratio does not include the cost of disk storage to store
the news or of computer time to process it; both of those are assumed to be
free.
The cost ratio is computed as follows:
$US/month/reader = ($USPerMonthPerSite * numberOfSites) / numberOfReaders
$USPerMonthPersite = KBytesTrafficPerMonth * $USPerKByte
$USPerKByte = ($USperMinute / KBytesPerMinute) * (1 - CompressionFactor)
$USperMinute = 0.10 [ten cents per minute avg phone cost]
KBytesPerMinute = 60 * BytesPerSecond / 1000
BytesPerSecond = 100 [average transfer rate over 1200-baud line]
CompressionFactor = 0.4 [40% compression is typical for netnews]
Combining all these gives
$USPerMonthPersite =
KBytesTrafficPerMonth * (0.10 / 6) * (1 - 0.4)
= KBytesTrafficPerMonth / 100
Therefore:
$US/month/reader =
(KBytesTrafficPerMonth * numberOfSites) / (100 * numberOfReaders)
The accuracy of this number is in fact better than the accuracy of the
participation ratio, because the source of error--the network size
estimate--is present both in the numerator and the denominator, and therefore
cancels out. The primary source of bias in this number comes from the bias in
the "estimated number of readers, worldwide", which is described above. Treat
this value as being accurate to within about 25%.
SITE PARTICIPATION
I would like to receive data from every site on USENET. The arbitron programs
(posted to net.sources along with this report) work on news 2.9, 2.10.[1-3],
2.11, and on many versions of notesfiles.
Brian Reid
DEC Western Research Laboratory, Palo Alto CA
reid@decwrl.DEC.COM
{ihnp4,allegra,decvax,ucbvax,sun,glacier}!decwrl!reid