reid@decwrl.UUCP (Brian Reid) (05/01/87)
USENET READERSHIP SUMMARY REPORT for Apr 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 complete set of readership data (of which this is a summary) is posted
in mod.newslists. The software that will let your site participate in the
survey is in net.sources.
Brian Reid
OVERALL SUMMARY:
This Estimated
Sample for entire net
Sites: 458 6500
Fraction reporting: 7.05% 100%
Users with accounts: 60526 859000
Netreaders: 12736 180000
Average readers per site: 28
Percent of users who are netreaders: 21.04%
Average traffic per day (megabytes): 2.001
Average traffic per day (messages): 910
Traffic measurement interval: last 21 days
Readership measurement interval: last 75 days
Sites used to measure propagation: 299
Valid data received from these sites:
1141g 3comvax 3d.dec.com 4gl 52494.dec.com aaec abel abstl
abvax.abnet.com acetes acornrc adelie advax.dec.com 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
asd.dec.com astroatc astrovax atari athena atssc ausmelb auspyr axis
babbage basser bcm5000 bdmrrr being.dec.com bellman beno bigbang bms-at
bnl boole brand brspyr1 btnix bu-cs bucasb bucket bucsb.bu.edu bucsd
buengc buit1.bu.edu bunker bute.tcom.stc.co.uk cacilj cad.dec.com
cadomin cadsys.dec.com caip.rutgers.edu calgary cascade casee.dec.com
castor.dec.com catsim cavell cbosgd cca cfisun cgl.ucsf.edu chaos
charlie chas2 chinet ci-dandelion cideq3 circe cisunx cit-vax cit-vlsi
clinet clio clt.dec.com cognos concurrent.co.uk cookie.dec.com cortex
cos cpro cpw.columbia.edu crcge1 crin cs.nott.ac.uk csadfa csm9a
csustan curium.dec.com cuuxb cvl cwruecmp cxsea dalcs dalton darth
davaar.tcom.stc.co.uk davasun dayton dciem dcl-cs decwrl delni.dec.com
desint devlab.dec.com devon dgis dhw68k diamond.bbn.com dievms.dec.com
dinadan dlb dssdev.dec.com dukempd dvlmarv dycom earvax ecc.dec.com
ector.cs.purdue.edu edison elbereth.rutgers.edu elrond elroy elsie ems
endor enea eneevax eplunix ernie.berkeley.edu eros esc-bb eta ethos
euler.berkeley.edu euraiv1 ewok.dec.com exodus.dec.com fai fedeva felix
fortune foxvax5 fritz gaia ganash garfield gatech geac genrad geocub
gidday.dec.com gitpyr glacier glass.dec.com gould9 grebyn grumpy
gt-stratus haddock.isc.com hammer hanyang hao harvisr hechcx hercules
hi hjuxa hoptoad hpcea hqda-ai hscfvax husc2 husc4 husc8 hvrunix
iapetus.rice.edu ichaya ico ileaf ima imagen imt3b2 indian.dec.com
infinet intrin invest iscuva ishtar isl islabs istg.dec.com
izimbra.css.gov jasper ji.berkeley.edu jimi.cs.unlv.edu jon.dec.com
jplgodo kefren killer kirk.dec.com kodak kolvi korppi labrea
ldp.dec.com leah leia lindy litp liuida lll-crg macbeth maccs mapper
masscomp maxwell maynard mcdchg mcgill-vision mck-csc me-ncr meccsd
meccts mejac mind minnow mirror mit-eddie mks mlfs1.dec.com mnetor
mntgfx monstr.dec.com mordred.cs.purdue.edu mosaic.dec.com moscom mss
mstar msudoc mtgzy mtgzz mtunb mtund mtune mtunf mtung mtunh mtuni
munsell myrias naakka nac.dec.com navajo nbifet nbires ncoast ncr-sd
ncrcae nears netrix.dec.com nexus.dec.com noao nttlab nucsrl nvanbc
oblio oblio.dec.com oddjob.uchicago.edu olamb olivea olivee olivej
oliven omepd onecom opus orca orion orion.arpa osi3b2 osiris osupyr
oulu panda pbhya pbhyc pbhyd pbhye pdn pdnbah pegasus percival phoenix
phoenix.princeton.edu phri piaget pixar plaid plus5 pogo popeye popvax
poseidon princeton psivax ptsfa pulman.dec.com pwcs pyramid pyrnova
pyrps5 qtc quad1 quoin.dec.com rayssd rayssdb rayssde reality1 remsit
renoir.berkeley.edu retix ritcv rlgvax rlpyr-a rlvc rlvd rochester
rocky rosevax rti-sel ruby sandoz saturn sauron scgvaxd scicom sdcsvax
sdn shark shasta sibelius sicsten sigma soma sphinx spock sqm.dec.com
sri-spam sstmv1.dec.com star.dec.com stb stl stride styx suadb
subsys.dec.com sunybcs tallis.dec.com teddy tekecs teklds tekred temvax
tesla teti thelink thundr.dec.com tipple.dec.com titan.rice.edu
tle.dec.com tmsoft topaz.rutgers.edu tove.dec.com tropix trwspf
turtlevax tutctl tutor tymix ub ubc-cs ubvax ucbarpa.berkeley.edu
ugdist uiucuxa uiucuxc uiucuxe uiucuxf ukma ulowell ultra.dec.com
umd5.umd.edu umn-d-ub umnd-cs-gw uncle.dec.com unsvax.uucp uqcspe.oz
ur-laser usc-oberon utacs utcs utcsri uw-warp uwmacc van-bc vianet
viking.dec.com vilya vino.dec.com violet.berkeley.edu viper virginia
voder voodoo vu-vlsi vulcan walldata wanginst watale watarts watcgl
watdaisy watdcsu watdragon wateng water watlion watmath watmum watnot
watopt watrose watvlsi wiley wnuxb wolf wp3b01 wuphys xios yarra yetti
yogi.dec.com zaphod zeus zgov01.dec.com 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 net.sources, 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
12 months worth of data.
There are 6423 different sites in the Path lines of articles that
arrived at decwrl in the last 12 months. There are 5206 different sites in
the mod.map data, but mod.map 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 6423 sites, 52 (0%) are DEC E-net hosts not part of
uucp, and which therefore are not included in the 5206 figure.
Despite these various difficulties, I believe that 6500 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