reid@decwrl.dec.com (Brian Reid) (08/01/87)
USENET READERSHIP SUMMARY REPORT for Jul 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: 505 7400
Fraction reporting: 6.82% 100%
Users with accounts: 71472 1047000
Netreaders: 14195 208000
Average readers per site: 28
Percent of users who are netreaders: 19.86%
Average traffic per day (megabytes): 2.501
Average traffic per day (messages): 1080
Traffic measurement interval: last 21 days
Readership measurement interval: last 75 days
Sites used to measure propagation: 387
Valid data received from these sites:
1141g 3comvax 52494.dec.com aaec abstl abvax.abnet.com acad academ
acetes acornrc adelie alberta alliant alv amdahl amdcad ames
amsterdam.columbia.edu ant.dec.com apollo apple aramis.rutgers.edu
argus armory.dec.com arran.tcom.stc.co.uk array arthur.cs.purdue.edu
ascvax astra astroatc atari atom atssc aurora auspyr axis b-tech
babbage banana.cs.uq.oz bandit.dec.com basser bdmrrr bellman beno
beowulf.ucsd.edu bigbang black bms-at bnl bnr-rsc boole boris brand
brand.usc.edu 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.berkeley.edu cadomin caip.rutgers.edu calgary calyx cantuar
cascade casee.dec.com catsim cavell cbosgd cbterra cca celica.dec.com
cesare.dec.com cfisun cgcha cgl.ucsf.edu chalmers charlie
charon.dec.com chas2 cheviot.newcastle.ac.uk chinet chovax.dec.com
ci-dandelion cideq3 cimcor circe cisunx cit-vax cit-vlsi clinet clio
cognos concurrent.co.uk cortex cos cpro crin crvax1.dec.com
cs.nott.ac.uk csadfa csm9a csuchic csustan cullvax curium.dec.com cuuxb
cvl cwruecmp cxsea dalcs dale dalton darth dasys1 davasun dayton dciem
dcl-cs ddsw1 decwrl decwrl.dec.com delni.dec.com desint devlab.dec.com
devon dgis dhw68k diamond.bbn.com dino dlb dopey drexel dukempd dvlmarv
dycom earvax ecsvax ector.cs.purdue.edu edison elbereth.rutgers.edu
elroy elsie ems endor enea eneevax.umd.edu eplunix erlang.dec.com
ernie.berkeley.edu eros ers eta ethz euler.berkeley.edu
euler.rutgers.edu euraiv1 exodus.dec.com fai fedeva felix
fermat.rutgers.edu fortune fritz g.ms.uky.edu garfield gatech
gatos.dec.com gauss.rutgers.edu geac genrad gii gilroy gitpyr glacier
grebyn gt-stratus gvgpsa gymble haddock.ima.isc.com haddock.isc.com
hadron hammer handel hao harvisr hechcx hi hoptoad hpcea hqda-ai
hscfvax husc4 husc8 hutch hvrunix iaoobel iapetus.rice.edu ichaya ico
ileaf ima imagen imt3b2 inco indian.dec.com infinet intrin invest
ipso.oz irs1 iscuva ishtar islabs itcatl izimbra.css.gov jasper
ji.berkeley.edu jimi.cs.unlv.edu jplgodo kaoa01.dec.com ki4pv killer
klinzhai.rutgers.edu kodak kolvi korppi kosman krebs labrea lakesys
leah.albany.edu leds.dec.com leia lemon.berkeley.edu lily lindy lion
liuida lll-crg lll-tis lognet2 lola lotus lzaz lznv lzsc lzwi macbeth
maccs majestix mapper marvin.dec.com mas1 masscomp maxwell maynard
mcdchg mcgill-vision meccsd meccts megatest mendel metavax mhres mimsy
mind minnow mit-eddie mnetor mntgfx mordred.cs.purdue.edu morris mss
mstar msudoc mtgzy mtunb mtund mtune mtunf mtung mtunh mtuni mtunj
mtunl mtxinu mulga munnari munsell myrias nac.dec.com navajo nbifet
nbires ncoast ncr-sd ncrcae ncsuvx necntc neptune newton.rutgers.edu
nibroc noao novavax ntassg nttlab nucsrl oberon oblio ocean
oddjob.uchicago.edu olamb olivea oliveb olivee olivej oliven omepd
onecom orca orchid orion.arpa osiris owf panda pasta.dec.com
paul.rutgers.edu pbhya pbhyb pbhyc pbhyd pbhye pcrat pdn pegasus
percival phoenix phoenix.princeton.edu phri piaget pixar plaid pluto
pogo popeye popvax poseidon psc psuvax1 ptsfa puck pvab pyr pyramid
pyrdc qetzal qiclab qtc quad1 quoin.dec.com ra rainbo.dec.com rayssd
rayssdb rayssde remsit renoir.berkeley.edu retix retort.dec.com
rhea.dec.com rlvc rlvd rochester rocky rose rosevax rti ruby
rutgers.rutgers.edu sandia sandoz saturn sauron scgvaxd scicom sdcsvax
sdn se-sd seiph shark shasta sibelius sics sigma sjfc sneaky
sniff.dec.com soma sonora sphinx spock sri-spam starfish stb stl styx
suadb sunybcs svo swan.cs.ulowell.edu teddy tekecs tekred temvax
terminus tesla teti tiger titan.rice.edu tmsoft toccata.rutgers.edu
topaz.rutgers.edu tropix trwspf tucos turtlevax tutctl tutor twitch
tybalt.caltech.edu tymix ub ubc-cs ubvax ucbarpa.berkeley.edu uccba
uhnix1 uhnix2 uiucuxa uiucuxc uiucuxe uiucuxf ukecc ulowell
ultra.dec.com umd5.umd.edu umix.cc.umich.edu uqcspe.oz ur-laser utacs
utradio uvabme uwmacc van-bc vaxtrain vianet vino.dec.com
violet.berkeley.edu viper virginia voder voodoo vrdxhq vu-vlsi vulcan
wanginst ward watale watarts watcgl watdaisy watdcsu watdragon wateng
water watmath watmum watopt watsol watt watvlsi well wheaton wiley
wnuxb wolf wp3b01 wrs xanth xios yarra yetti z.dec.com zaphod
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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 7384 different sites in the Path lines of articles that
arrived at decwrl in the last 13 months. There are 3670
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 7384 sites,
31 (0%) are DEC E-net hosts not part of uucp, and
which therefore are not included in the 3670 figure.
Despite these various difficulties, I believe that 7400 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