Subgroup Size Research Articles

SBRT Versus Sublobar Resection for Stage I NSCLC

National guidelines recommend surgery, ideally lobectomy, as the preferred treatment for stage I NSCLC. For patients who cannot tolerate lobectomy, sublobar resection can be considered but is known to be associated with a higher risk of disease recurrence. We sought to compare our institutional experience with SBRT and sublobar resection in stage I NSCLC. We also evaluated pre-treatment factors that may be associated with a higher risk of local failure after SBRT. As part of an IRB-approved retrospective study, data was collected on patients treated at our institution for stage I NSCLC between 2007 and 2014. SBRT was delivered using 3-5 fractions to a total dose of 48-60 Gy. All surgical patients underwent a wedge resection or segmentectomy, typically with hilar and mediastinal lymph node sampling/dissection. Patients undergoing lobectomy or pneumonectomy were excluded. Clinical data including patterns of failure were collected. The primary endpoint of interest was progression-free survival, defined as date of treatment to date of disease recurrence or death from any cause, with patients censored at the time of last follow-up, estimated using the Kaplan-Meier method. Freedom from local recurrence and overall survival were also assessed. 85 patients undergoing SBRT and 53 patients undergoing sublobar resection (surgery) were compared. The SBRT cohort was older (72 vs 67 years, p=0.008), had worse pulmonary function (FEV1 50% vs. 64%, p=0.001; DLCO 50% vs. 60%, p=0.037), and had larger tumors (2.4 vs 2 cm, p=0.003) with higher SUVmax values (10.4 vs 6.8, p=0.005). The median Charleson co-morbidity index was 3 with SBRT and 1 with surgery (p<0.05). With a median follow-up of 2 years, progression-free survival at 2 years for SBRT and surgery cohorts was 72% versus 78%, (p=0.23). On multivariate analysis, the only factor that was significantly associated with inferior progression-free survival was Charleson comorbidity index (HR 1.28, 95%CI 1.09-1.51, p=0.003), with SUVmax trending toward significance (HR 1.04, 95%CI 0.99-1.09, p=0.06). Treatment approach (SBRT versus surgery) was not significant on multivariate analysis (p=0.228). Local control (89% at 2 years in both, p=0.31) and overall survival (88% surgery vs 97% SBRT, p=0.18) were comparable. Within the SBRT subgroup, SUVmax and tumor size were associated with a higher risk of local failure after SBRT on univariate analysis. However, on multivariate analysis the only factor that remained significant was SUVmax (HR 1.12, 95% CI 1.01-1.24, p=0.035) assessed as a continuous variable. Comparing SBRT and surgery is challenging given differences in known prognostic factors between cohorts. Progression-free survival appears to be comparable between both approaches. With far less morbidity than surgery, SBRT is an attractive alternative to sublobar resection in patients not eligible for lobectomy. SUVmax may be an important metric predicting for a higher risk of local failure after SBRT.

Female Spider Monkeys (Ateles geoffroyi) Cope with Anthropogenic Disturbance Through Fission-Fusion Dynamics.

Most primates live in habitats with some level of anthropogenic disturbance, and such disturbances have a larger impact on frugivorous primates that are more sensitive to ecological disruptions than folivores. Fecal glucocorticoid metabolites provide insight into how the external environment affects internal physiological state, and thus provide information on how anthropogenic pressures become embodied. Here, I examine how subgroup size and glucocorticoids vary with high and low fruit abundance, and how fruit abundance, subgroup size, and activity budget affect fecal glucocorticoid metabolites in female spider monkeys (Ateles geoffroyi) living in an anthropogenically disturbed habitat. I measured these variables via behavioral, ecological, and fecal sampling for 15 months in 17 female spider monkeys at El Zota Biological Field Station. Subgroup size was significantly larger during periods of high fruit abundance, but glucocorticoids did not differ between periods of low and high fruit abundance. Monthly fruit abundance predicted subgroup sizes significantly, but did not predict fecal glucocorticoid concentrations. Increased resting time and reproductive state predicted fecal glucocorticoid concentrations significantly, but travel and foraging time had no significant effect on glucocorticoid concentrations. Individual resting time over the study period correlated negatively with glucocorticoid concentrations. These results suggest that spider monkeys cope with variation in fruit abundance by adjusting subgroup size, and that these adjustments may mitigate environmental stress in this mildly seasonal environment. The large, relatively productive forest size at this site, and the availability of anthropogenic food sources, enable this population of spider monkeys to cope with human-induced habitat disturbance.

Identifying consistent statements about numerical data with dispersion-corrected subgroup discovery

Existing algorithms for subgroup discovery with numerical targets do not optimize the error or target variable dispersion of the groups they find. This often leads to unreliable or inconsistent statements about the data, rendering practical applications, especially in scientific domains, futile. Therefore, we here extend the optimistic estimator framework for optimal subgroup discovery to a new class of objective functions: we show how tight estimators can be computed efficiently for all functions that are determined by subgroup size (non-decreasing dependence), the subgroup median value, and a dispersion measure around the median (non-increasing dependence). In the important special case when dispersion is measured using the mean absolute deviation from the median, this novel approach yields a linear time algorithm. Empirical evaluation on a wide range of datasets shows that, when used within branch-and-bound search, this approach is highly efficient and indeed discovers subgroups with much smaller errors.

Shewhart dispersion charts made easy for mild to moderately autocorrelated normally distributed data

ABSTRACTThe aim is to make it easier for users to implement dispersion monitoring plans when the data are autocorrelated. If the data follow a low-order ARMA model then the same threshold for the monitoring plan is applicable by revising the rational subgroup size. A robust plan for non-normal data is achieved in most cases by first transforming the data to an approximate normal distribution, and then applying the plan for normally distributed data. The dispersion plan is based on the robust regression estimator of the slope coefficient when regressing the ordered rational sub-group values against their “expected” in-control values.

How Big Should My Dot Be? Using Spreadsheet Simulation to Evaluate Process Improvement Data Collection Strategies

Occasionally, healthcare professionals approach analytical topics and courses with a blend of fear and loathing. They may fail to grasp the connection between particular principles and their application to actual process analysis and improvement. The run chart is a persuasively powerful quantitative tool. Healthcare teams could use this tool to better comprehend the extent of process changes over time. Although constructing the run chart is mathematically simple, healthcare professionals may be uncertain as to sample size sufficiency. They may also be unsure of the number of observations required in run chart subgroups. We developed a spreadsheet simulation model to provide enhanced relevance for the topic of run chart subgroup size determination. This classroom-tested active learning exercise helps healthcare teams to visually understand the relationships between subgroup size, underlying process variation, and anticipated levels of improvement.

Relationship quality affects fission decisions in wild spider monkeys (Ateles geoffroyi)

AbstractFission–fusion dynamics are thought to be mainly a response to differential availability of food resources. However, social factors may also play a role. Here, we examined whether the quality of social relationships between group members affects fission decisions. During 21 months, we collected data on social interactions and fission events of 22 spider monkeys (Ateles geoffroyi) living in a community in the protected area of Otoch Ma'ax Yetel Kooh, Yucatan, Mexico. By entering seven indexes of social interactions into a principal component analysis, we obtained three components of relationship quality, which we labelled “compatibility,” “value” and “insecurity” given the relative loadings of the indexes. Our results showed that individuals were more likely to fission into the same subgroup with community members with whom they shared higher levels of compatibility and value and lower levels of insecurity. In addition, individuals preferred to fission into the same subgroup with same‐sex group members, as expected based on what is known for the species. Our findings highlight the role of social factors in fission decisions. Adjustments in subgroup size are based on multifaceted social preferences, incorporating previously unexamined aspects of relationship quality, which are independent from overall levels of affiliative interactions.

Perceiving crowd attention: Gaze following in human crowds with conflicting cues.

People automatically redirect their visual attention by following others' gaze orientation, a phenomenon called "gaze following." This is an evolutionarily generated socio-cognitive process that provides people with information about their environments. Often, however, people in crowds can have rather different gaze orientations. This study investigated how gaze following occurs in situations with many conflicting gazes. In two experiments, we modified the gaze cueing paradigm to use a crowd rather than a single individual. Specifically, participants were presented with a group of human avatars with differing gaze orientations, and the target appeared randomly on the left or right side of a display. We found that (a) when a marked difference existed in the number of avatars with divergent gaze orientations, participants automatically followed the majority's gaze orientation, and (b) the strongest gaze cue effect occurred when all gazes shared the same orientation, with the response superiority of the majority's oriented location monotonically diminishing with the number of gazes with divergent orientations. These findings suggested that the majority rule plays a role in gaze following behavior when individuals are confronted with conflicting multigaze scenes, and that an increasing subgroup size appears to enlarge the strength of the gaze cueing effect.

Three-dimensional trajectories and network analyses of group behaviour within chimney swift flocks during approaches to the roost.

Chimney swifts (Chaetura pelagica) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers from surrounding areas near a roost site. The whole flock then employs an orderly, but dynamic, circling approach pattern before rapidly entering a small aperture en masse. We recorded the three-dimensional trajectories of ≈1 800 individual birds during a 30 min period encompassing flock formation, circling, and landing, and used these trajectories to test several hypotheses relating to flock or group behaviour. Specifically, we investigated whether the swifts use local interaction rules based on topological distance (e.g. the n nearest neighbours, regardless of their distance) rather than physical distance (e.g. neighbours within x m, regardless of number) to guide interactions, whether the chimney entry zone is more or less cooperative than the surrounding flock, and whether the characteristic subgroup size is constant or varies with flock density. We found that the swift flock is structured around local rules based on physical distance, that subgroup size increases with density, and that there exist regions of the flock that are less cooperative than others, in particular the chimney entry zone.

Phase II control charts for monitoring dispersion when parameters are estimated

ABSTRACTShewhart control charts are among the most popular control charts used to monitor process dispersion. To base these control charts on the assumption of known in-control process parameters is often unrealistic. In practice, estimates are used to construct the control charts and this has substantial consequences for the in-control and out-of-control chart performance. The effects are especially severe when the number of Phase I subgroups used to estimate the unknown process dispersion is small. Typically, recommendations are to use around 30 subgroups of size 5 each. We derive and tabulate new corrected charting constants that should be used to construct the estimated probability limits of the Phase II Shewhart dispersion (e.g., range and standard deviation) control charts for a given number of Phase I subgroups, subgroup size and nominal in-control average run-length (ICARL). These control limits account for the effects of parameter estimation. Two approaches are used to find the new charting constants, a numerical and an analytic approach, which give similar results. It is seen that the corrected probability limits based charts achieve the desired nominal ICARL performance, but the out-of-control average run-length performance deteriorate when both the size of the shift and the number of Phase I subgroups are small. This is the price one must pay while accounting for the effects of parameter estimation so that the in-control performance is as advertised. An illustration using real-life data is provided along with a summary and recommendations.

Analysis of the Effect of Subgroup Size on the X-Bar Control Chart Using Forensic Science Laboratory Sample Influx Data

This paper analyzes the effect of subgroup size on the x-bar chart characteristics using sample influx (SIF) into forensic science laboratory (FSL). The characteristics studied include changes in out-or-control points (OCP), upper control limit UCLx, and zonal demarcations. Multi-rules were used to identify the number of out-of-control-points, Nocp as violations using five control chart rules applied separately. A sensitivity analysis on the Nocp was applied for subgroup size, k, and number of sigma above the mean value to determine the upper control limit, UCLx. A computer code was implemented using a FORTRAN code to create x-bar control-charts and capture OCP and other control-chart characteristics with increasing k from 2 to 25. For each value of k, a complete series of average values, Q(p), of specific length, Nsg, was created from which statistical analysis was conducted and compared to the original SIF data, S(t). The variation of number of out-of-control points or violations, Nocp, for different control-charts rules with increasing k was determined to follow a decaying exponential function, Nocp = Ae–α, for which, the goodness of fit was established, and the R2 value approached unity for Rule #4 and #5 only. The goodness of fit was established to be the new criteria for rational subgroup-size range, for Rules #5 and #4 only, which involve a count of 6 consecutive points decreasing and 8 consecutive points above the selected control limit (σ/3 above the grand mean), respectively. Using this criterion, the rational subgroup range was established to be 4 ≤ k ≤ 20 for the two x-bar control chart rules.

Do Fruit Nutrients Affect Subgrouping Patterns in Wild Spider Monkeys (Ateles geoffroyi)?

One of the main costs of group living is feeding competition. Fission–fusion dynamics are thought to be a strategy to avoid overt competition for food resources. We tested whether food abundance and quality affected such dynamics in a species characterized by a high degree of fission–fusion dynamics. We collected data on 22 adult and subadult spider monkeys (Ateles geoffroyi) living in a large community in the protected area of Otoch Ma’ax Yetel Kooh, Yucatan, Mexico. We recorded subgroup size and fission events as well as fruit abundance during 12 mo and conducted nutritional analyses on the fruit species that the study subjects consumed most. We found no effect of fruit abundance or nutritional quality of recently visited food patches on individual fission decisions, but the amount of protein in the food patches visited over the course of the day was a good predictor of subgroup size. While the absence of support for a relationship between fruit characteristics and fission decisions may be due to the short temporal scale of the analysis, our findings relating subgroup size to the amount of protein in the visited food patches over the course of the day may be explained by individual spider monkeys attempting to obtain sufficient protein intake from their fruit-based diet.

Fission-fusion dynamics in black-and-white ruffed lemurs may facilitate both feeding strategies and communal care of infants in a spatially and temporally variable environment

Species with greater expression of fission-fusion dynamics show greater variability in the size, composition, and cohesion of subgroups over time. This may allow their adjustment to local environmental, social, and demographic conditions. We tested which environmental and social factors influenced subgroup size in one such species, the black-and-white ruffed lemur (Varecia variegata) at two sites within a fragmented forest landscape. Using instantaneous focal sampling at 15-min intervals, we collected data on subgroup size and composition, fruit and flower availability, and location. We also collected biweekly data on site-wide fruit and flower availability. We used these data to test the influence of season, food availability, reproduction, and predation risk on adult subgroup size in this species. Ruffed lemur adults consistently formed significantly larger subgroups in times of lower site-wide fruit availability, during the wet season, and when one or more infants were present. There were differences between sites in the relationship between subgroup size and tree size, fruit patch size, and site-wide flower availability. Variables measuring indirect predation risk showed no significant relationship with subgroup size. These results emphasize the strong relationship between fission-fusion dynamics and spatial and temporal variation in food availability, as well as the importance of sociality in a species with communal care of infants. Fission-fusion dynamics may serve as an evolutionary strategy to adapt to the unpredictable and sometimes harsh environmental conditions of Madagascar and may facilitate the persistence of communities of this critically endangered lemur despite widespread anthropogenic habitat modification. Fission-fusion dynamics (the joining and separating of subgroups within a larger group of animals) may allow species to adjust social benefits to changing environmental conditions. This study examines the underlying ecological and social factors that might influence fission-fusion dynamics in black-and-white ruffed lemurs. Subgroup size in this species was strongly related to food availability, though not always in the direction expected. This suggests that the relationship between food availability and sociality changes when food availability reaches very low levels. Additionally, infant presence was linked to larger adult subgroups, indicating a connection between fission-fusion behavior and the cooperative rearing of offspring seen in this species. Relationships between subgroup size and some environmental variables differed between sites, emphasizing the flexibility of grouping patterns in this species and indicating that local conditions may play a large role in the expression of fission-fusion dynamics.

Vocal correlates of individual sooty mangabey travel speed and direction.

Many group-living animals coordinate movements with acoustic signals, but so far most studies have focused on how group movements are initiated. In this study, we investigated movement patterns of wild sooty mangabeys (Cercocebus atys), a mostly terrestrial, forest-dwelling primate. We provide quantitative results showing that vocalization rates of mangabey subgroups, but not of focal individuals, correlated with focal individuals’ current movement patterns. More interestingly, vocal behaviour predicted whether individuals changed future speed, and possibly future travel direction. The role of vocalizations as a potential mechanism for the regulation of group movement was further highlighted by interaction effects that include subgroup size and the quality of poly-specific associations. Collectively, our results suggest that primate vocal behaviour can function beyond travel initiation in coordination and regulation of group movements.

Sex, Age, and Graft Size as Predictors of ACL Re-tear

Objectives:The minimum size required for a successful quadrupled hamstring autograft ACL reconstruction remains controversial. The risks of ACL re-tear in younger patients who tend to participate in a higher level of sports activity, and female athletes who have numerous predisposing factors, are poorly defined. Purpose: To identify risk factors for graft re-tears within 2 years of ACL surgery. The hypotheses are that female sex, a smaller size graft, and younger patients will increase the odds of failure. Study Design Cohort Study. Level of evidence, 3.Methods:A cohort of 503 athletes undergoing primary, autograft hamstring ACL reconstruction, performed by a single surgeon using the same surgical technique and rehabilitation protocol, between September-December 2012, was followed for a total duration of 2 years. Return to play was allowed between 6 and 12 months post-surgery upon completion of functional testing. Exclusion criteria included infections, revisions, double bundle techniques, multi-ligament injuries, non-compliance, BTB/allografts/hybrid grafts. Primary outcome consisted of binary data (ACL graft re-tear or no tear) as measured on physical exam (Lachman and pivot shift) and MRI. Multivariate logistic regression statistical analysis with model fitting was used to investigate the predictive value of sex, age, and graft size on ACL re-tear. Secondary sensitivity analyses were performed on the adolescent subgroup, age and graft size as categorical variables, and testing for interactions among variables. Sample size was calculated based on the rule of 10 events per independent variable for logistic regression.Results:The mean age of the 503 athletes was 27.5 (SD 10.6; range = 12-61). There were 235 females (47%) and 268 males (53%) with a 6% rate of re-tears (28 patients; 17 females). Mean graft size was 7.9 (SD 0.6; range = 6-10). Univariate analyses of graft size, sex, and age only in the model showed that younger age (odds ratio [OR] = 0.86; 95% confidence interval [CI] = 0.80-0.93; P = .001] and smaller graft size (OR = 0.36; 95% CI = 0.18-0.70; P = .003) were significantly predictive of re-tear. Female sex was correlated with re-tear but was not significant (OR = 1.8; 95% CI = 0.84-3.97; P = .13). Multivariate analysis with all 3 variables in the model showed similar significant results. Graft size < 8 mm (OR = 2.95; 95% CI = 1.33-6.53; P = .008) and age < 25 (OR = 7.01; 95% CI = 2.40-20.53; P = .001) were significantly predictive of re-tear. Entire model was statistically significant (Omnibus test P = .001; Hosmer-Lemeshow statistic P = .68; Receiver Operating Curve [ROC] = 0.8).Conclusion:Surgeons should counsel their patients who are female, younger than 25 and with a graft size less than 8 mm accordingly and consider modifying their surgical or rehabilitation techniques to mitigate these re-tear risks.

Monitoring multivariate process variability when sub-group size is small

ABSTRACTThe current practice of multivariate process variability monitoring, when sub-group size is small, has nothing to do with probability of false alarm (PFA). Consequently, the reliability of the existing control charts remains undetermined. In this article, we propose a control chart which is reliable, very sensitive to the change in variance for small or moderate correlation, and provides a root causes analysis of an out-of-control signal. To illustrate these advantages, an industrial example is presented and the results are compared with those issued from the existing methods.

Seasonal Changes in Socio-Spatial Structure in a Group of Free-Living Spider Monkeys (Ateles geoffroyi).

Ecological and social factors influence individual movement and group membership decisions, which ultimately determine how animal groups adjust their behavior in spatially and temporally heterogeneous environments. The mechanisms behind these behavioral adjustments can be better understood by studying the relationship between association and space use patterns of groups and how these change over time. We examined the socio-spatial patterns of adult individuals in a free-ranging group of spider monkeys (Ateles geoffroyi), a species with high fission-fusion dynamics. Data comprised 4916 subgroup scans collected during 325 days throughout a 20-month period and was used to evaluate changes from fruit-scarce to fruit-abundant periods in individual core-area size, subgroup size and two types of association measures: spatial (core-area overlap) and spatio-temporal (occurrence in the same subgroup) associations. We developed a 3-level analysis framework to distinguish passive associations, where individuals are mostly brought together by resources of common interest, from active association, where individuals actively seek or avoid certain others. Results indicated a more concentrated use of space, increased individual gregariousness and higher spatio-temporal association rates in the fruit-abundant seasons, as is compatible with an increase in passive associations. Nevertheless, results also suggested active associations in all the periods analyzed, although associations differed across seasons. In particular, females seem to actively avoid males, perhaps prompted by an increased probability of random encounters among individuals, resulting from the contraction of individual core areas. Our framework proved useful in investigating the interplay between ecological and social constraints and how these constraints can influence individual ranging and grouping decisions in spider monkeys, and possibly other species with high fission-fusion dynamics.

Spatial Consensus Queries in a Collaborative Environment

We introduce a new type of query for a location-based social network platform. Consider a scenario in which a group of users is trying to find a common meeting location, yet attempting to include all group members is introducing a significant traveling cost to most of them. In this article, we formulate a new query type called the consensus query , which can be used to help users explore these trade-off options to find a solution upon which everyone can agree. Specifically, we study the problem of evaluating consensus queries in the context of nearest neighbor queries, where the group is interested in finding a meeting place that minimizes the travel distance for at least a specified number of group members. To help the group in selecting a suitable solution, the major challenge is to find optimal subgroups of all allowable subgroup sizes, i.e., greater or equal to the minimum specified subgroup size, that minimize the travel distances. We develop incremental algorithms to evaluate in one pass the optimal query subgroups of different sizes along with their corresponding nearest data points. These subsets, which are evaluated by the location-based service provider, constitute the answer set that is returned to the group. The group then collaboratively selects the final answer from the candidate answer set. An extensive experimental study shows the efficiency and effectiveness of our proposed techniques.

Watch out or relax: conspecifics affect vigilance in wild spider monkeys (Ateles geoffroyi)

In most animal species, predation risk is considered the main factor affecting vigilance, and an individual is expected to spend less time vigilant in larger than in smaller groups. However, vigilance patterns in primates appear to differ, with no consistency in group-size effects. As individuals in highly gregarious species such as diurnal primates face frequent threats from group members, there may be increased vigilance in larger groups to monitor conspecifics rather than or in addition to predators. We tested this hypothesis in wild spider monkeys, which live in communities but fission and fuse in subgroups of variable size and membership throughout the same day. We found no overall effect of subgroup size, as traditionally measured, on vigilance. However, a possible explanation is that vigilance may be effectively shared only with individuals in close proximity, rather than with all subgroup members. We found that a larger number of neighbours (i.e., subgroup members within 5 m) was associated with a lower proportion of time individuals spent vigilant, which is similar to findings in other studies. Another social factor that may affect individuals’ vigilance is the possibility of between-community encounters. Higher levels of vigilance can be expected in areas closer to the boundary of the home range, where between-community encounters are more likely to occur compared with non-boundary areas. We found that location in terms of boundary vs. non-boundary areas had a significant effect on the time individuals spent vigilant in the expected direction. We also found that location modulated the effect of subgroup size on vigilance: only in the boundary areas did larger subgroup sizes result in less individual vigilance time. We concluded that conspecifics affect vigilance of wild spider monkeys in multiple ways.

Process Capability Analysis of a Centre Lathe Turning Process

A process capability study is performed for the turning process on a general purpose center lathe in order to verify the process performance and machine ability to perform within specified tolerance limit. The process and machine capability indices were measured to determine the process and machine adequacy for industrial application. The tolerance limits were obtained from the given nominal size of the shaft, using the basic hole system and 90 sample shafts were turned on the lathe machine to specification for varying spindle speed and feed rate of the lathe. Three (3) samples were randomly selected for the turning process of a combination of the spindle speed and feed rate as a subgroup size for a total subgroup of thirty (30). The diameters (representing the quality characteristics) were used to generate control charts and capability histogram for the process. The process is within statistical control but found incapable of meeting up to specification because the capability index (Cp) measured was less than 1 and the machine capability for industrial application is not adequate.

Resource seasonality and reproduction predict fission-fusion dynamics in black-and-white ruffed lemurs (Varecia variegata).

Ruffed lemurs (genus Varecia) are often described as having a flexible social organization, such that both cohesive (low fission-fusion dynamics) and fluid (high fission-fusion dynamics) grouping patterns have been observed. In ruffed lemur communities with high fission-fusion dynamics, group members vary in their temporal and spatial dispersion throughout a communally defended territory. These patterns have been likened to those observed in several haplorrhine species that exhibit the most fluid types of fission-fusion social organization (e.g., Pan and Ateles). To substantiate and further refine these claims, we describe the fission-fusion dynamics of a black-and-white ruffed lemur (Varecia variegata) community at Mangevo, an undisturbed primary rainforest site in Ranomafana National Park, Madagascar. We collected instantaneous group scan samples from August 2007-December 2008 (4,044 observation hours) to study and characterize patterns of subgroup size, composition, cohesion, and social association. In 16 consecutive months, we never found all members of the community together. In fact, individuals spent nearly half of their time alone. Subgroups were small, cohesive, and typically of mixed-sex composition. Mixed-sex subgroups were significantly larger, less cohesive, and more common than either male-only or female-only subgroups. Subgroup dynamics were related to shifts in climate, phenology of preferred fruit species, and female reproductive state. On average, association indices were low. Males and females were equally gregarious; however, adult male-male associations were significantly weaker than any other association type. Results presented herein document striking differences in fission-fusion dynamics between black-and-white ruffed lemurs and haplorrhines, while also demonstrating many broad-scale similarities to haplorrhine taxa that possess the most fluid fission-fusion societies.