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. monthly signup in x10³ users nAg20 u 01 otl Ssgu eito rmisse its from A deviation curve. - signup gray 2004 CS Jan as Monthly in fit signup 2011. function total Aug power CS - for 2009 fits Aug function in Power 3. Figure m over HC+CS chart for Pie HC+CS. search and Google CS of HC, for distribution volume mean search adjusted Google 2. Figure Total signup in millions of profiles Google search volume in % of CS maximum

0 1 2 3 4 5 6 7 8 9 11 13 15 17 19 0 20 40 60 80 100 Jul 10.6% Jun 9.1% Aug 11.3% u 4Ag0 u 6Ag0 u 8Ag0 u 0Ag1 u 2Aug 13 Aug 12 Aug 11 Aug 10 Aug 09 Aug 08 Aug 07 Aug 06 Aug 05 Aug 04 40 60 80 01 21 415 14 13 12 11 10 09 08 07 06 05 04 May 7.8% CS HC HC+CS Monthly signup deviation Fit for Aug 2009−Aug 2011 Fit for Jan 2004−Aug 2011 Real datafor CStotalsignup Sep 8.7% Apr 7.6% CS databasecrash Mar 7.9% Oct 7.9% Feb 7.2% Nov 7.4% August 20.. Jan 7.4% Dec 7.1% onths. g21 and 2011 ug asonalized fgrowth of

−100 −50 0 50 100

Monthly signup deviation from seasonalized power function fit in % is seasonal and growing. Using Box-Cox transformation [14], we can fit a power function to HC+CS. Averaging the deviations between HC+CS and the fitting power function Google 27405 gives us a growth adjusted average distribution of interest in Microsoft 15181 hospex services over months. August has the highest share Yahoo 8933 GMX 2527 with 11.3% and December the lowest with 7.1%. The five Other .com−domains 1929 Web.de GmbH 1359 months Jun–Oct have almost the same share as Nov–May. Mail.ru Group 1160 Other .net−domains 933 Therefore we use August to mark the time axis on all plots. Other .de−domains 897 Educational organizations 847 This seasonality in Google search volume is common for all Orange 545 Yandex 448 travel services like Airbnb or Booking.com. La Poste 435 freenet group 431 You see on fig.2 that the interest in CS overtook HC in Wirtualna Polska 408 2007, whereby the interest in HC started to decrease. Both AOL 368 Alternative emailproviders 363 curves show seasonal variations with peaks in August. The Other .org−domains 316 Other .it−domains 289 seasonal variations for HC distinctly and visibly flattened Italiaonline 286 Other .fr−domains 256 from August 2009 on. The growth of the monthly signup for Apple 204 Tencent QQ 197 CS decreased from August 2009 on as well. The gray curve Other .pl−domains 193 Other .cz−domains 190 on fig.3 shows the deviation between the CS monthly signup Other .ch−domains 156 and its seasonalized power function fit. On this curve, you Rambler&Co 145 Other .co.−domains 144 see the chasm of the CS database crash in summer 2006 and Others 1485 the clear slowdown after August 2009. This slowdown caused the change in the slope of the total signup curve for CS as 1 10 100 1000 10000 depicted on fig.3. The two power function fits, meaning for Jan 2004 - Aug 2011 and for Aug 2009 - Aug 2011, shape different predictions. The growth of CS users dropped to almost quadratic from being over cubic before August 2009. Figure 4. Domain name categorization and corresponding histogram in absolute numbers. By the way, the power function fit after August 2009 gives a prediction of 6.9M users for Dezember 2013. Since CS and HC are equivalent services, we assume a user migration period in the years 2006-2009, which powered the faster universities and schools from all around the world make 1.2%. growth of CS and the decline of HC. We have introduced the category of alternative providers, The self-proclaimed purpose of the first hospex service which emphasize privacy and/or certain political goals. These Servas is “world peace, goodwill and understanding by are riseup.[org|net], no-log.org, lavabit.com, biomail.de, spam- providing opportunities for personal contacts among people freemail.de, openmailbox.org, jpberlin.de, mailoo.org, safe- of different cultures, backgrounds and nationalities” [4]. mail.net, immerda.[ch|de] and posteo.*. This category makes CS adapted it as “a better world – one couch at time” [8]. only .5% of all signups. Although signing up at BW is driven Combining World Bank and CS data reveals that 75% of the by incorporation of CS and its consequences, majorities choice world population, which lives in poor countries with a per in email providers is not be explained as ethically dictated. capita GDP under $10,000, represented only 10% of CS users Not every signup at BW leads to subsequent real life in 2011. Well, at least for CS the admission to the ’better interaction. 4921 out of 68030 profiles never logged in after world’ seems to be tightly restricted by income level. signing up. Fig.5 makes a picture of this fact. The rate of users, who did never log in, grew with those signing up after September 2011 and stays at around 10%. The incentives for logging in on a hospex website are searching a stay, V. INSIGHTS FOR BW replying a request and general communication. We consider The growth of interest in BW does not display seasonal posting, inviting and contacting members for organization of variation as it is obvious on Fig.5, but rather is driven by activities and other minor reasons as examples for general protest of CS users. There is a major peak in BW signups communication. A user interested only in hosting, would not and the google search volume in September 2011 – CS has have any incentive to log in until an appropriate hospitality been secretly privatized for the personal enrichment of a few request is forwarded to his e-mail postbox. If communication a month before [15]. The three peaks between August 2012 obviously stimulates login frequency, one is interested in what and August 2013 are also consequences of changes in CS, is stimulating communication. which have been considered to be unethical by CS community. Under the application of decision tree based feature The first of these peaks is caused by the update in CS ToU, selection [16], we could determine two factors, which have according to which the CS data can be sold to third parties. most impact on number of received messages, in case neither A data set of 68320 profile entries has been received from messages have been sent nor posts have been published. These BW on 04.03.2014. 68030 of those entries possess e-mail do- factors are the indicated gender and the hosting status. Fig.6 main names – local parts have been removed before data trans- shows the average number of messages received depending on action concerning privacy. The remaining 290 entries are either these two factors. The profile text was not under investigated invalid or officially deleted. Fig.4 shows the domain name cat- features, because it has been replaced by its length to beware egorization and the corresponding histogram. E-mail services users’ privacy. For your information, 41.7% of BW users administrated by Google, Microsoft and Yahoo make 75.4% of indicated to be female and 56.7% to be male. all signups. Domain names of educational organizations like Users, who set their hosting status on “No, sorry” are iue6 vrg ubro esgsrcie,i ete se neither if received, messages of number Average 6. Figure rate. login’ ’no and growth BW 5. Figure BW Google search volume and signup in % of maximum Yes, Welcome

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, Average number of real life connections 1]J vror .Wlzn n .Pts Tutpropagati “Trust Potts, C. and n Wulczyn, trust E. for Overgoor, model J. generative and “Analysis [12] Dandekar, P. [11] 1]P itr .Crei,M .Cc,adE Herrera-Viedm E. and Cock, D. M. Cornelis, C. Victor, P. [10] o ellf neatosi Wcmuiyvrae between variates community BW 5. in number and average interactions 3 The life hours. 15 24 real and within for needed, probability were same messages the hospitali archive average for 10 To an 04.03.2014, traveler. for before at week a request lacks within BW probability reply providers. appl 96% ethic e-mail not unethical about do of concerns be utilities choice users’ to facilitating BW communication considered with hospex Most are community. of correlates CS but which the seasonal, CS, by not of is changes BW major in interest The 2009. 1]G .P o n .R o,“naayi ftransformation of analysis “An Cox, R. D. and Box P. E. G. [14] 1]D atrah .Tun,T hh n .A dmc “Sur Adamic, A. L. and Shah, T. Truong, H. Lauterbach, D. [13] eas hn h epe h rvddteWk irr [16]. library Weka express the help provided their to who for people, want Bevolunteer the of I thank also co-members [17]. We the License to gratitude Commons my Creative a under 1]Bvlnerog ‘opxdt eerh n ‘bewelc and research’ data “‘hospex Bevolunteer.org, [17] 1]I .Wte n .Frank, E. and Witten H. I. 2 couchwiki.org, issues,” [16] ‘conversion’ “Couchsurfing [15] 9 Apiwrd”api-ol.e,2014. aupair-world.net, “Aupairworld,” couchsurfing.org. [9] inc.” “Couchsurfing [8] 7 .Shit Hsiaiycu:Ntwr ie tr¨aumer eines Netzwerk club: “Hospitality Schmidt, J. [7] 6 .Sletzk Hse aaaefritrainle international for database a - “Hospex Sylwestrzak, W. deutsch.hospitalityclub.org/ab [6] club,” “Hospitality servas.org/who-we-are.php. [5] international,” “Servas [4] 2 .Sylla, A. [2] [1] 3 .J ue,“atesi n ieecag mn h es the among wife-exchange and “Partnership Rubel, J. A. [3] hswr a atal ulse nBewelcome.org on published partially was work This cetfi rceig eiso optrEgneigadI and Engineering Science Computer on Series Proceedings Scientific es,2006. Reise, fet oes”in models,” effects ae grgto prtr o rda rs n distrust and trust gradual for operators aggregation based optlt o rvles”hospex.org. travellers,” for hospitality 09 p 346–353. pp. 2009, lu fnrhr ot mrc, in america,” Alaska north of University northern of aleut fteRylSaitclSceySre B Series Society Statistical 1964. Royal the of ftut euainadrcpoiyo couchsurfing.com,” on reciprocity and Reputation trust: of eecm.r/ii pi 2014. April bewelcome.org/wiki, utn i ae:HwA-ad sWnigteWro Terror on War the Winning 2008. Is Schultheis, Al-Qaeda How Laden: Bin Hunting hee,Uiestd il I,1980. III, Lille de Universit th`eses, 00 p 505–510. pp. 2010, , apioohemrl e Wolof des morale philosophie La A OTAND BOUT ICWSM 91 p 59–71. pp. 1961, , R EFERENCES 2012. , A aaMining Data CKNOWLEDGMENT nhoooia aeso the of papers Anthropological ognKumn,2005. Kaufmann, Morgan . o.2,n.2 p 211–252, pp. 2, no. 26, vol. , tle erdcindes Reproduction Atelier . outdeu.htm. , pee Online Spiegel s,” 011. nwt mixed- with on etworks.” m charts’,” ome ,“Bilattice- a, ”in ,” in cag of xchange s,” nformation n web a fing ioand kimo S (4) CSE Journal Rob . World on y ty . ,