» Cornell Info 204 - Networks NSDL.org > Expert Voices > Cornell Info 204 - Networks Larger Text Cornell Info 204 - Networks This is a supplemental blog for a course which will cover how the social, technological, and natural worlds are connected, and how the study of networks sheds light on these connections. Google to Connect Friends Across the Web Thursday, May 15th, 2008 11:42 pm Contributed by: xiaotu As if social networking craze weren’t spreading across the globe quickly enough, Google recently announced a new service  - Friend Connect – that can turn any website into a social networking site. All the webmasters have to do is add “ a snippet” of code to their page and Google takes care of the rest.  No matter how obscure a site is, it can still allow its users to meet and connect without the hassle of signing up for a whole new account. Innovative, or inevitable? The implications of a company with as much influence as Google promoting this idea are huge – it can’t be hard to imagine in just the next few years, a social networking site (powered by Google!) that connects all pages of internet. However, I’m curious as to exactly how this system can work. Part of the premise of launching this project is previous user complaints that sites such as Facebook and MySpace require you to be within the site to connect with friends. How will Google circumvent this?  I know I for one tend to browse site like Facebook using my own profile as “home base.” In any case, I don’t feel Facebook should be too worried yet – I know I will still prefer my already-establish “closed” community of college friends and all my nifty applications, although I’m sure I’ll tap into “Friend Connect” at some point for some of my more obscure hobbies… like duct-tape wallet making. The Google engineers themselves point out that the venture is more “’about helping the ‘long tail’ of sites become more social’.” What exactly this will do to the dynamic of the internet is yet to be seen, but I can bet that the impact won’t be small. In the meantime, it could be fun to keep an eye on FAS.research . Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Containing Violence and Spreading Masculinity in Chicago Friday, May 9th, 2008 9:34 am Contributed by: tkrueger Tim Krueger               The cover article of Sunday’s New York Times Magazine explores the mechanics of a new approach to gang conflict on Chicago’s south side, in doing so weighing the logic behind regarding violence as a sort of virus.  Alex Kotlowitz explains how Gary Slutkin, the architect of CeaseFire in Chicago, plots out a strategy that is informed by his experiences managing diseases like Cholera and HIV.  The idea behind the organization is that violence also spreads through social networks, one incidence fueling others by way of the human desire for retribution.  Efforts to prevent violence should therefore be aimed at the points of probable transmission, in effect containing the violence.  As with a disease, the earlier one can isolate the source, the less likely something menial is to spiral into an epidemic.             Slutkin and his colleagues in Chicago’s CeaseFire have thus decided to use their combined cerebral map of the city’s social networks as the canvas for their violence-prevention strategy.  The logic here is impeccable; it moves beyond older approaches that are ideologically inspired and lack focus, and it puts to use the intellectual capital that is probably the group’s greatest asset.  Yet really, the group is attempting to harness Chicago’s social network for two opposite objectives.  As the title suggests, the Violence Interrupters play an anti-diffusion role, blocking the spread of the violence that might otherwise spread outward.  At the same time, however, they try to catalyze a positive diffusion throughout those networks, offering alternative constructs of masculinity to those they visit.  That is, to convince likely vengeful individuals not to escalate conflict, the CeaseFire workers need to provide a set of masculine norms that doesn’t contradict such behavior.  The hope is that this alternative masculine construct will spread in exactly the same manner that violence would have.  The extent to which Slutkin envisions his organization as pursuing this positive diffusion is unclear; while he raises issues of behavior-spreading as central to dealing with violence and other epidemics, he seems to regard the organization’s relationship to social networks as an inherently interjectory one.             The distinction between these two opposing goals is important for a few reasons.  First, it provides the potential for a self-perpetuating cycle, or behavioral cascade.  When the group only works to retard the spread of something, it is always fighting an uphill battle.  With the chance of offering its own behavior for diffusion, it might be able to craft a long-term plan that does not always depend on the presence of such an organization.  The success of such a cascade, it seems, would depend on whether alternative constructs of masculinity are diffusing at a higher rate than violence is perpetuating.  If not, the prospects of a sustained counter-masculinity are dim.  In the article, this concept of underlying fragility plays out in the constant fear of relapse among the Violence Interrupters.  And on a broader scale, the extent to which a successful cascade might breach the boundaries of Chicago depends largely on the social linkages between Chicago and other cities, and the level of exposure needed for such behavior to spread. Second, the diffusion-encouraging mission might imply different strategies than the violence-intervening approach alone.  For instance, instead of simply targeting individuals recently affected by violence, the organization might target the most socially embedded norm-setters regardless, and peddle their new-masculinity there.  This would mean contacting a different set of individuals, but might be associated with more effective or efficient results for the norm-spreading objective.  And as in the question of a potential cascade, it might be found that these two type of diffusion have different thresholds for catching on, again possibly necessitating different strategies for each.             Also, an assessment of a neighborhood’s social density might have implications for which of these two goals might find more success.  In the presence of incredibly dense social networks, it might be difficult to locate and quickly intervene at all of the points to which retributive behavior is likely to take hold.  However, in such an instance, it might be possible to locate a small number of people who are densely linked to large numbers of others, and who therefore might be effective positive norm-spreaders. If spreading norms for alternative masculinities can only be achieved in the context of potential violence, it may not be possible to fully disaggregate these two tasks.  It does seem that they do not always go hand in hand though.  In one instance when a Violence Interrupter mediated a brooding conflict by paying a gang leader $300, it surely seems that the negative role was achieved without mitigating any conceptions of masculinity.  If nothing else, mere conceptual differentiation between these two roles might have implications for whether or not it makes sense to use women as Violence Interrupters.  While women may be able to successfully mediate conflict, it seems less likely that their forte would be in constructing and spreading norms of masculinity. In fact, this point probably hits at the heard of any success CeaseFire has had at either goal.  It seems clear that both roles have depended upon the organization’s capacity to attract individuals who are themselves well-linked within these social networks.  Defining the concept of “insider,” and determining whether there exists any difference in this term for the organization’s negative-diffusion positive-diffusion roles, may shed light whether or not those two tasks can or should be disaggregated. Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Braess for Closures: A New Take on City Congestion Friday, May 9th, 2008 8:04 am Contributed by: econ204blogger http://query.nytimes.com/gst/fullpage.html?res=9C0CE7D81530F936A15751C1A966958260&scp=1&sq=Braess’Paradox&st=cse Much to the chagrin of many New Yorkers, Mayor Michael Bloomberg announced a widespread traffic proposal that would charge people $8 to enter Manhattan below 86 th Street. While many praised Bloomberg for his plan—estimated to bring New York City $500M—most said that the toll would encumber New York City businesses. For months, the mayor has been pitted against the city council trying to negotiate a compromise. From what we have learned in Networks this semester, I think the answer is clear: close down streets in Manhattan. While the idea sounds preposterous, a similar strategy worked in 1990. In honor of Earth Day in 1990, City Commissioner Lucius Ricco decided to shut down 42 nd Street—one of Manhattan’s most congested streets. “Many predicted it would be doomsday,” Ricco recounted. Yet, Dr. Ricco was armed with two invaluable tools: a doctorate degree in engineering and a knowledge of Braess’ paradox. Mathematician Dietric Braess discovered that adding extra capacity to a network might actually slow it down. He proved his theory using a diamond shaped model. Dotting the model, were four nodes on each point of the diamond. In order to get from Town A to Town D, one could either choose routes AB, BD or AC, CD. Each had a specific value of time that it would take to travel each road. The time it took to traverse AB or CD was dependent upon the total number of cars on the road divided by 100. Roads AC and BD, however, were constant at 45 minutes. On a normal day, if 4000 cars decided to drive from Town A to D, we could assume that 50 would take route AB and 50 would take AC. In total, travel would take 65 minutes for each route. Now, suppose we dropped a perpendicular route from B to C. This new road is covered with some new synthetic asphalt which takes drives no time at all to travel from B to C. While this might sound like a time saver, it is not. All 100 cars on the road are likely to take this new route, but instead of 65 minutes, it will now take 80 minutes! So, contrary to popular belief, adding more does not always beget less. The reason why Braess was correct is clear. Every driver gets selfish and looks for the quickest possible route. However, since everyone is thinking the same thought, the route will become more congested. And, since traffic speeds are a function of capacity, the more cars on the road, the slower the traffic. For instance, I am frequently stuck in traffic while crossing the George Washington Bridge. Often, the lane to my left is moving more briskly than my lane. So, I decide to change lanes only to find that many people in my lane have decided the same thing! The lesson is that if local politicians lobby for street closures they should be met with cheers and not jeers! Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Incorrigible Information: The Housing Bubble and Information Cascades Friday, May 9th, 2008 8:02 am Contributed by: econ204blogger http://www.nytimes.com/2008/03/02/business/02view.html?pagewanted=2&_r=1&sq=information%20cascade&st=nyt&scp=1 One of my father’s favorite jokes is “What is the state bird of Florida? The construction crane!” For a time, I believed that the joke was more of a fact than a mere quip. Driving up A1A, a major thoroughfare that runs parallel to South Florida’s beaches, revealed hundreds of new condominium development project each soaring higher than the other. Yet, I could not help but wonder who would occupy these gargantuan structures. The short answer to my quandary was no one. The recent bubble in the housing market hit Florida especially hard because of the large amount of Real Estate speculation. The recent burst of the housing bubble was presupposed by a tremendous information cascade. An information cascade occurs when rational individuals imitate the actions of others when their information suggests an alternative choice. Basically, an information cascade can be summed up by utterance “They must know something I don’t.” Sadly, this type of mentality usually occurs before major market turmoil like the housing bubble. Information cascades were an all to familiar part of the tech bubble of 2000. As the Dow and NASDAQ propelled upward quicker than rockets, many people risked their savings betting on a ’sure thing.’ As people watched their friends and family invest money in the burgeoning stock market, they began to believe that others had more knowledge than they did, despite knowing that investing is inherently risky. It is easy to let something go when just the Jone’s do it, but when the Jone’s, Smith’s, Doe’s all do something collectively, they must be on to something. The housing bubble marks a similar denouement. “I’d come to realize that we’d never be able to identify irrational exuberance with certainty, much less act on it, until after the fact,” said former Federal Reserve Chairman Allan Greenspan. In fact, researchers have been able to calculate this risk, claiming, cascades lead to incorrect assumptions 37% of the time. With respect to the housing market, who could blame people for thinking Real Estate was a lucrative investment? With apartments in Manhattan fetching upwards of $20M and a new crop of television shows geared to flipping houses, the real estate market seemed ripe. However, what people did not know is that many of these homes were being purchased through risk adjustable rate mortgages that locked unknowing home buyers into a temporary teaser rate that floated with the prime. Once interest rates rebounded, people could not afford to make their mortgage payments and defaulted on their loans. Since a new glut of real estate hit the market and demand plateaued, housing prices plummeted. An old adage in elementary school warned that what is popular is not always right. Such a phrase can describe an information cascade; however, it is quite difficult to go against the grain. Information cascades remind me of Solomon Asch’s famous experiment. Asch drew three vertical lines of differing length on a chalkboard. He then asked people to identify the longest line. His sample size was contaminated, however, as he planted confederates within the experiment that were told to submit the wrong verbal answer. The experimental subject—who had no knowledge the other’s were in on the trick—almost always agreed with the incorrect answer. Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Is It Worth It? Network Effects and Private Institutions Friday, May 9th, 2008 7:57 am Contributed by: econ204blogger http://www.nytimes.com/2006/12/13/education/13voices.html?pagewanted=2&sq = Upon completion of this four-course meal they call college, Cornell University will stick me with a bill totaling $200,000. The price of college education—especially at private institutions—has been the subject of much media attention as of late. Institutions such as Harvard, Princeton, and Yale have instituted bold programs providing free education for students who cannot afford tuition. Earlier this month, Provost Martin outline a similar program here at Cornell. These programs only deal with the beginning of the financial issue vexing many parents across America. Even after financial aid, student loans, and scholarships, a private college education can cost as much as a house. For example, Jenny Russel, an alumna of the University of Redlands prides herself on her private educate despite the $50,000 in debt she received along with her degree. Those, like Ms. Russel, who note a marked difference between public and private schools cite the network effects produced by private education. In a normalized market, the laws of supply and demand function fluidly. However, network effects examine how networks function when a good or service’s potential value to customers depends upon the number using it. For example, telephones would be relatively worthless if many people chose not to purchase them. The same goes for computer operating systems. The fact that there is an integrated network of telephone users justifies the value of purchasing a phone and paying for service. Yet, for the purchaser to assess how much he/she will pay for the object, he/she must predict the total number of users of the good. When examining colleges, this term of “users of the good” can be quite vacuous. However, as the article suggests, we can bifurcate the users of the good to general educational experience and resulting job opportunities. While many like Cal State University’s President, F. King Alexander claim that private institutions have a Chivas Regal affect—having an aesthetic facade, but nothing special internally—a private institution does exhibit network effects. We must be clear, however, the variable cannot be expressed in ‘how many’ use the service, but rather who uses the service. The selectivity is the most desired attribute of private institutions. A group of students is winnowed into an entering class representing the supposed pinnacle of applicants. The perceived benefit of a private education is the ability to be around students of similar caliber thereby creating a cocoon of higher learning that will benefit all. The second variable is who used the good before, meaning what types of alumni and networking do schools afford. I can only speak for Cornell on this matter, unfortunately. Having gone through an on-campus recruitment process and subsequent internship, I can personally attest to the benefit of private school networks. For example, perhaps the most qualified candidate in my analyst class, attends a state school in New Jersey. One day, several analysts from private colleges were discussing how easy on-campus recruitment was. Unfortunately, my friend from the state school did not have it as easy as we. He spent most of his time cold calling banks, sending faxes and resumes, and networking consistently. When examining the price tag of private universities, one must ask, why would anyone pay such astronomical fees when cheaper alternatives exist? The answer lies in the network effects of private institutions. Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. The Spread of The West Coast Offense Thursday, May 8th, 2008 8:39 pm Contributed by: woodford As an assistant with the Cincinatti Bengals, Bill Walsh developed an offense strategy called the West Coast offense. This system used multiple receiver sets and short, precise passing that countered the traditional football strategies of run-based offenses and downfield passing. Walsh later became head coach of the San Francisco 49ers and won three Super Bowls with this innovative offense. He created one of the most prolific offenses of all time with legendary players such as Joe Montana and Jerry Rice. Because of its enormous success, many other head coaches began to adopt the West Coast offense to try to replicate the success of Walsh’s famous team. The spread of this system illustrates many aspects of network theory, including power laws and the diffusion of innovation. The small-world phenomenon of football coaches is a well known fact, but the West Coast offense did not spread just from Walsh’s protégés. Many other head coaches with no relation to Walsh adopted the West Coast system, or at least elements of it, including such respected coaches as Brian Billick and Mike Martz. The West Coast offense appealed to many coaches looking for an explosive offense. As more coaches replicated Walsh’s success with system, the offense grew immensely popular among head coaches at all levels, especially in the college game, which it is particularly suited for. Following power law distribution, its popularity became self-reinforcing as coaches copied the offense after observing the success of others with it. Even coaches with players ill-suited for running the West Coast offense adopted it thinking that they too could have the same success as Walsh. Football is an ideal environment to observe power laws. In the cutthroat business of football, coaches are always looking for an edge on the competition, the next innovative formation or play. There is a lot of pressure on football coaches to succeed; their very job depends on it. So it is not surprising that there is much imitation in the NFL, college football, and even high school football. In fact, the NFL is well known as a copycat league. This trend has been around for decades, ever since Sammy Baugh popularized the forward pass in the 1930s with the Redskins. http://espn.go.com/nfl/s/westcoast/history.html Posted in Topics: General , Social Studies Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Gaming the System: Are Hedge Fund Managers Talented, or Just Good at Fooling Investors? Thursday, May 8th, 2008 5:02 pm Contributed by: am494 Hedge funds are small aggressively run funds that use advanced strategies and advanced derivatives to produce high returns in either absolute marks or market bench marks. The $2 trillion hedge fund market brings around questions about their power, performance, and economic impact. Compared to the highly regulated mutual funds, the secretive and mostly unregulated hedge funds can bring around problems to people investing in hedge funds because their strategies aren’t necessarily as descriptive and stern. Recently there has been new substantial research by Wharton statistics professor Dean P. Foster and Brookings Institution senior fellow H. Peyton Young about the statistics of hedge funds and how managers of these small and secretive, and mostly unregulated funds, can use statistics in their favor and convince investors that their profitable yields might be larger and more appealing than what they really are. Their comparison of the hedge fund market to a lemon market is riveting because of the huge power that hedge funds have in the financial world. Also, with the huge yields that hedge funds produce for the managers, with about 1% to 2% of assets and up to 20% of returns. The publication in Knowledge@Wharton and a research article “The Hedge Fund Game: Incentives, Excess Returns, and Piggy‐Backing” at Wharton Business School explored the incentives and tactics that hedge fund managers could possibly use to in a sense “scam” high-risk investors. The underlying issue within lemon markets is the idea of scamming consumers into believing that there are more “good” products than there are “bad” products, driving consumers to make decisions based on probabilities. “‘According to Mr. Foster and Mr. Young, investing in a hedge fund is like buying a ‘lemon’ — a car with hidden flaws. ‘This is a potential ‘lemons’ market in which lemons can be manufactured at will, and the lemons look good for a long time before their true nature is revealed.’” (DealBook Blogs, NYtimes) The market for lemons that we covered in lecture stated that the limited information when deciding to make a purchase in a market with varied quality of products produces this market of uncertainty for the consumer. When the seller knows the quality of specific products, they have different values for the products than the buyers do. There is some sort of scamming principles in this idea as naturally sellers and buyers want to get the most profit possible, but the sellers have more information, therefore usually profit more. Then the idea of assumptions and probabilities of assumptions and how these probabilities affect consumers’ decisions comes into play. “At first glance, hedge funds appear to load management contracts with incentives to encourage good performance and to keep managers’ interests in line with investors’. But in practice, there is no way to encourage excellence without making scamming profitable as well. ‘The main claim of our paper is there is no way to write an incentive contract which will differentiate the two,’ Foster said.” (Knowledge@Wharton) This statistical research showed the ways that managers could possibly manipulate investors more than highly regulated mutual funds. It does not mean that every hedge fund manager is trying to scam their investors, but in a world of money and greed and trying to get the greatest profit, it is interesting to compare the hedge fund sector to a lemon market. sources: http://knowledge.wharton.upenn.edu/papers/1352.pdf http://knowledge.wharton.upenn.edu/article.cfm?articleid=1931&CFID=58584308&CFTOKEN=13228094&jsessionid=a8302864a51c13425137 http://dealbook.blogs.nytimes.com/2008/04/03/hedge-funds-a-lemon-market/ Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Diseases and Network Theory Tuesday, May 6th, 2008 5:45 pm Contributed by: rcp32 What first struck me about this article (http://www.nytimes.com/2008/05/06/health/research/06dise.html?_r=1&ref=science&oref=slogin) from today’s New York Times was the similarity of the diagram of diseases organized by the genes that cause them to say any other network diagram we have studied in class. While the bulk of the article deals with the changing paradigm of how disease are thought of, classified and treated, the concepts learned in this class especially as it relates to network theory seem to be applicable. The notion that the treatment of a disease is not longer the binary “cause and effect” model, but more “rhizome” based is an interesting advance. The fact that the network model of genes can let alone be understood but used in this way is significant advancement in the field of human knowledge. These new links between seemingly different diseases can lead to new advances in medicine, but also illustrate the fragility of any given network. The fact that these disease which were before not considered to be related illustrates that the break down in any part of the network can lead to unexpected results. While this information will possibly lead to a complete reclassification of diseases and a new approach to how diseases are combated, what should not be overlooked is this notion of fragility. The fragility of the network and the way information is transmitted and effects other parts of the network that makes us up is so vast and still unknown, that given the fact that now we can act on this scale of the human body, is there any way to see what repercussions this might have on how we are formed? In other words, is there any way to know what the effects of manipulating the genetic foundation could have on the future of our species? This in now way means that this research is not valid in the discourse of medicine, but perhaps by applying the seemingly unrelated field of network theory, answers to these and other questions could be postulated. Posted in Topics: Education Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Diffusion Simulation Game Tuesday, May 6th, 2008 3:20 pm Contributed by: rcp32 This online simulation game (http://www.indiana.edu/~istdemo/) created by the University of Indiana, has at its heart, the premise of exploring how information is transmitted across a network. By using a created narrative of getting different teachers at a fictional high school to adopt a new pedagogical technique, it focuses many topics of discussion including the way information is transmitted, the importance of how it is transmitted and the role that people who have already adopted it play in its propagation. However, what interests me more than perhaps the game as an exploration of the effect of these phenomena, is the notion of being able to translate a qualitative effect into a quantitative values. The question for me that arise is how does one translate human behavior as seen in the “wild” into a strictly defined set of rules for a program to then generate answers from. While I cannot begin to discuss the mechanics of how this information is then modeled into a computer program, the ability of a computer to do this brings up questions as to what defines us as humans. If a computer can be programmed to act as a human would act, or at least be able to predict how a given human would react to certain information, does that make the computer human, or does it make us simply computer programs running simultaneously. These ethical or ontological questions that arise from the translation of the concepts learned in this class into practice are ones that, in and of themselves, could fill up another semester. The helpfulness of the simulation, which is in my opinion, excellent, in transmitted the concepts is not the issue I want to bring up, but rather, how the advance of this types of simulation affect the way we understand our place in the world around us. As computer seem to take over various aspects of over lives that we once under direct human control, it allows us time to explore other realms of our existence. While this increased “technologification” is something that we should not (or perhaps cannot) stop, the problems it brings up run deeper that the pure mechanics of how to make it a reality. It in fact seems that, as this program is for me an example, that due to the ability of technology to increasingly models complex “natural” phenomena while at the same time take over tasks that once occupied our time, a redefinition of what our place in our context is in order. Posted in Topics: Social Studies , Technology Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. Drug Epidemics and Network Theory Monday, May 5th, 2008 10:31 pm Contributed by: woodford In 2001, The National Institute of Justice released a report on drug epidemics and warned of a new marijuana epidemic that had begun in the 1990s. Through extensive research, the Institute discovered an alarming rise in marijuana usage among the nation’s youth. This trend could have serious implications, including precipitating an increase in so-called “hard drugs” such as cocaine and heroine, according to the idea that marijuana is a gateway to other more dangerous drugs. On the other hand, the decline in hard drug usage supports the theory that the nation’s youth have replaced more harmful drugs, such as crack, with marijuana. Researchers note how this new marijuana epidemic is similar in nature to previous drug epidemics. The report explains how a drug’s popularity follows a bell-curve trajectory: starting out slow, growing exponentially, leveling off, and then dying down. Previous drug epidemics, including the widespread marijuana usage in the late 1960s and early 70s and the destructive crack epidemic of the late 1980s, reflect this cycle. Drug epidemics demonstrate the diffusion of innovation in a social network. It starts with a small group of drug users and spreads like a virus through the network, infecting other nodes as it grows in popularity. These early adopters cause a cascade in the community where many others begin to use the drug as well. For this reason, drug epidemics seem to explode on the scene and seemingly come from nowhere, as was the case with the 1980s crack epidemic. The report also notes the importance of local differences in the spread of the epidemic. The life cycle of the drug scourge is wildly different in various communities and locations: sometimes severe and long-lasting, sometimes mild and short-lived, and sometimes not occurring at all. This fact underscores the significance of local differences, especially the cascade threshold and structure of the network in the spread of the drug epidemic. The marijuana craze forty years ago illustrates the life cycle of an epidemic and shows how it was able to spread within certain communities. In the tumultuous Vietnam era, marijuana became the drug of choice for the so-called “hippie movement” and the rebellious anti-war set. Originating in a small group of drug-users, it spread to college campuses and towns across the country, popularized in part by musical groups who promoted its use. The drug became socially acceptable in many communities but was shunned in others. The epidemic leveled off as it reached an equilibrium among users and non-users. After the war ended, changes in social mores and the aging of the Baby Boomers, its primary users, led to a decline in the popularity of marijuana. http://www.ncjrs.gov/txtfiles1/nij/187490.txt Posted in Topics: Health , Social Studies Add a Comment » These icons link to social bookmarking sites where readers can share and discover new web pages. « Previous Entries Sign In Information About Categories Bookmarks Education General Health Mathematics Science Social Studies Technology Bookmarks Cornell INFO 204 Digest Blog NSDL website Previous Posts May 2008 April 2008 March 2008 February 2008 January 2008 May 2007 April 2007 March 2007 February 2007 January 2007 Expert Voices Help Expert Voices User Feedback Syndicate RSS Feed Help with feeds Expert Voices 1.0 powered by: Content distributed under: Sign In | NSDL.ORG | Contact | Help | Privacy | Funded by NSF