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Fears that YouTube recommendations radicalize users are overblown, but social media still host and profit from dubious and extremist content.

The diffusion of networked information and communication technologies has facilitated the rise of novel modes of online collective action, collaboration, and public goods production. In this dissertation, I elaborate an interactional account of online collective action, emphasizing the role of micro-level social interactions in shaping organizational dynamics and collective behavior. This approach provides a clearer explanation of both the means by which individuals and groups within online collectives establish stable patterns of activity as well as the mechanisms through which those patterns change over time. The argument proceeds through a series of interconnected empirical studies of several different domains of online collective action including crowdsourcing labor markets, Wikipedia, and the U.S. political blogosphere. Across these studies, I find that interactions and interactional dimensions of behavior play a central role in mobilizing, retaining, and organizing participants engaged in online collective action. Interactional motives and incentives not only mobilize participation in online collectives, they also contribute to the emergence and persistence of participation patterns and organizational forms. The character of these inequalities and organizational forms vary widely, likely contributing to the uneven impact of online collectives.

This paper presents a study of gatekeeping in the U.S. political blog "Daily Kos." Open online collectives like Daily Kos use relational mechanisms, such as gatekeeping, to manage organizational boundaries and filter the contributions of participants. However, neither prior theories of gatekeeping nor the existing analyses of open online collectives account for the character or implications of gatekeeping in the Daily Kos community. Using qualitative evidence as well as statistical analysis of a large sample of comment threads on the site from 2008, I argue that gatekeeping on Daily Kos takes centralized and decentralized forms, and that both modes depend critically on relational boundary work among site participants. Centralized gatekeeping proceeds through actions by high-status members of the community. Decentralized gatekeeping, by contrast, consists of more numerous and small-scale interactions between community members, who filter and moderate each other's participation. Both forms of gatekeeping enhance the ability of site leaders and incumbent community members to regulate access to privileges and agenda-setting responsibilities on the site. These findings imply that the egalitarian ethos of open online collectives exists in tension with the mechanisms through which participation and status inequalities emerge among participants. How collectives engaged in mobilization and discursive production resolve this tension will shape the long-term impact of online participation and blogs on the political and public spheres.

In this article, the authors compare the practices of discursive production among top U.S. political blogs on the left and right during summer 2008. An examination of the top 155 political blogs reveals significant cross-ideological variations along several dimensions. Notably, the authors find evidence of an association between ideological affiliation and the technologies, institutions, and practices of participation. Blogs on the left adopt different, and more participatory, technical platforms, comprise significantly fewer sole-authored sites, include user blogs, maintain more fluid boundaries between secondary and primary content, include longer narrative and discussion posts, and (among the top half of the blogs in the sample) more often use blogs as platforms for mobilization. The findings suggest that the attenuation of the news producer-consumer dichotomy is more pronounced on the left wing of the political blogosphere than on the right. The practices of the left are more consistent with the prediction that the networked public sphere offers new pathways for discursive participation by a wider array of individuals, whereas the practices of the right suggest that a small group of elites may retain more exclusive agenda-setting authority online. The cross-ideological divergence in the findings illustrates that the Internet can be adopted equally to undermine or to replicate the traditional distinction between the production and consumption of political information. The authors conclude that these findings have significant implications for the study of prosumption and for the mechanisms by which the networked public sphere may or may not alter democratic participation relative to the mass mediated public sphere.

Online communities, like Wikipedia, produce valuable public information goods. Whereas some of these communities require would-be contributors to create accounts, many do not. Does this requirement catalyze cooperation or inhibit participation? Prior research provides divergent predictions but little causal evidence. We conduct an empirical test using longitudinal data from 136 natural experiments where would-be contributors to wikis were suddenly required to log in to contribute. Requiring accounts leads to a small increase in account creation, but reduces both high- and low-quality contributions from registered and unregistered participants. Although the change deters a large portion of low-quality participation, the vast majority of deterred contributions are of higher quality. We conclude that requiring accounts introduces an undertheorized tradeoff for public goods production in interactive communication systems.

Some of the most popular websites depend on user-generated content produced and aggregated by unpaid volunteers. Contributing in such ways constitutes a type of generous behavior, as it costs time and energy while benefiting others. This study examines the relationship between contributions to a variety of online information resources and an experimental measure of generosity, the dictator game. Results suggest that contributors to any type of online content tend to donate more in the dictator game than those who do not contribute at all. When disaggregating by type of contribution, we find that those who write reviews, upload public videos, write or answer questions, and contribute to encyclopedic collections online are more generous in the dictator game than their non-contributing counterparts. These findings suggest that generous attitudes help to explain variation in contributions to review, question-and-answer, video, and encyclopedic websites.

BACKGROUND: Articular cartilage defects of the knee can significantly impair function among young, high-demand patients. There are several techniques for chondral restoration, including osteochondral allograft transplantation (OCA), that may alleviate pain and re-create the native anatomy. However, clinical outcomes among athletic cohorts are limited. PURPOSE: To evaluate the efficacy and functional outcomes of OCA for medium to large osteochondral defects of the knee in physically active United States military servicemembers. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A military health care database was queried to identify all OCA procedures performed between January 2009 and March 2013. Inclusion criteria were army personnel with a minimum of 2 years' follow-up. Exclusion criteria included incomplete follow-up, inaccurate coding, and nonmilitary status. Variables of interest included sex, age, lesion location, grade and size of the lesion, body mass index, tobacco use, preoperative and postoperative visual analog scale (VAS) scores for pain, and presence of perioperative complications. Overall failure was defined as the inability to return to preoperative functional activities because of persistent knee complaints (clinical failure) or a revision cartilage procedure or arthroplasty (surgical failure). RESULTS: A total of 61 patients (52 male; mean age, 31.7 years) were identified, with a mean 46.2-month follow-up. The mean VAS pain score improved from 4.10 ± 2.17 preoperatively to 2.68 ± 2.73 postoperatively (P < .0009), and only 6 (9.8%) required a subsequent revision chondral procedure. Overall, 39 patients (63.9%) were able to return to a level of activity that allowed for the completion of military duties. Risk factors for clinical failure were preoperative body mass index, preoperative pain as measured on the VAS, and moderate to severe postoperative pain on the VAS. The risk factor for surgical failure was the presence of a complication. Risk factors for overall failure were the ...

BACKGROUND: Although the most common injury mechanism for pectoralis major (PM) tears is an eccentric loading mechanism typically caused by bench pressing, within the military, there is a unique injury mechanism associated with airborne operations. The results of operative repair for these parachute-induced PM tears have not been previously reported. PURPOSE/HYPOTHESIS: To assess the functional outcomes in military servicemembers undergoing operative repair of parachute-induced PM tears. We hypothesized that functional recovery would be impaired with delayed surgical intervention. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Included were active duty military servicemembers who underwent operative repair for PM tears caused by a parachute-induced mechanism. Charts were reviewed to identify characteristic, injury, and surgical variables. Patients completed the functional outcome assessment with the Disabilities of the Arm, Shoulder and Hand (DASH) and the American Shoulder and Elbow Surgeons (ASES) questionnaires. Outcomes were compared between patients treated within 6 weeks of injury and those treated beyond 6 weeks. RESULTS: Of the 68 identified PM tears, 25 were the result of parachute-induced mechanisms. A total of 13 patients consented and completed the functional outcome assessment. The mean patient age was 30.6 ± 6.4 years, and the mean follow-up period was 5.46 ± 1.26 years. Ten patients underwent repair within 6 weeks of injury, and the remaining 3 patients underwent repair at a mean of 338 days after injury (95% CI, -42.8 to 718.8 days), a significant difference between groups (P = .006). All 13 patients were able to return to military duties at a mean of 6 months from injury. Patients treated within 6 weeks of injury had significantly higher functional outcomes (DASH score, 6.17 vs 26.67; P = .018; ASES score, 85.97 vs 49.5; P = .008), with greater strength performance compared with preinjury (bench press, 90.58% vs 38.95%; P = .0057; push-ups, 81.9% vs 23.8%; P = .023) compared with ...

BACKGROUND: Pectoralis major (PM) tendon tears are common injuries in athletic patient populations, where operative repair is largely recommended for maximum functional recovery. The repair varies in difficulty and technique based on the location of the tear within the muscle-tendon unit. Magnetic resonance imagining (MRI) has been reported to be sensitive and specific for identifying the tear location, but the effect of injury mechanism on tear pattern has not been previously investigated. PURPOSE: To examine PM tears in a military patient population and assess the effect of injury mechanism (weightlifting vs high-energy trauma) on the tear pattern and accuracy of MRI interpretation. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Active duty military servicemembers undergoing operative repair of PM tendon tears with corresponding preoperative MRIs from 2 medical centers were identified. Two musculoskeletal fellowship–trained radiologists reviewed imaging studies, reporting the location of the tear within the muscle-tendon unit and the severity of the tear (sternal head vs clavicular head vs both). Radiographic findings were compared against intraoperative findings. Mechanism of injury and timing from injury to imaging and surgery were assessed to determine whether they affected the accuracy of MRI interpretations. RESULTS: A total of 72 patients were included (mean ± SD age, 33.7 ± 7.0 years; 100% male). Mechanisms of injury consisted of 46 weightlifting injuries and 26 high-energy injuries. Interrater reliability was poor for tear location (kappa, 0.162; P = .003) but substantial for extent of tear (kappa, 0.637; P < .0001). MRI had a 51.3% sensitivity and 63.6% specificity for identifying complete tears. MRI had a sensitivity of 73.9% and specificity of 72.2% for avulsion injuries and sensitivity of 75% and specificity of 79.3% for musculotendinous injuries. Mechanism of injury had no effect on extent of the tear but did affect the location of the tear, with a higher rate of avulsion injuries ...