Bayesian compositional regression with microbiome features via variational inference.

The microbiome plays a key role in the health of the human body. Interest often lies in finding features of the microbiome, alongside other covariates, which are associated with a phenotype of interest. One important property of microbiome data, which is often overlooked, is its compositionality as it can only provide information about the relative abundance of its constituting components. Typically, these proportions vary by several orders of magnitude in datasets of high dimensions. To address these challenges we develop a Bayesian hierarchical linear log-contrast model which is estimated by mean field Monte-Carlo co-ordinate ascent variational inference (CAVI-MC) and easily scales to high dimensional data. We use novel priors which account for the large differences in scale and constrained parameter space associated with the compositional covariates. A reversible jump Monte Carlo Markov chain guided by the data through univariate approximations of the variational posterior probability of inclusion, with proposal parameters informed by approximating variational densities via auxiliary parameters, is used to estimate intractable marginal expectations. We demonstrate that our proposed Bayesian method performs favourably against existing frequentist state of the art compositional data analysis methods. We then apply the CAVI-MC to the analysis of real data exploring the relationship of the gut microbiome to body mass index.

Skin microbiome alters attractiveness to Anopheles mosquitoes.

BACKGROUND: Some people produce specific body odours that make them more attractive than others to mosquitoes, and consequently are at higher risk of contracting vector-borne diseases. The skin microbiome can break down carbohydrates, fatty acids and peptides on the skin into volatiles that mosquitoes can differentiate. RESULTS: Here, we examined how skin microbiome composition of women differs in relation to level of attractiveness to Anopheles coluzzii mosquitoes, to identify volatiles in body odour and metabolic pathways associated with individuals that tend to be poorly-attractive to mosquitoes. We used behavioural assays to measure attractiveness of participants to An. coluzzii mosquitoes, 16S rRNA amplicon sequencing of the bacteria sampled from the skin and gas chromatography of volatiles in body odour. We found differences in skin microbiome composition between the poorly- and highly-attractive groups, particularly eight Amplicon Sequence Variants (ASVs) belonging to the Proteobacteria, Actinobacteria and Firmicutes phyla. Staphylococcus 2 ASVs are four times as abundant in the highly-attractive compared to poorly-attractive group. Associations were found between these ASVs and volatiles known to be attractive to Anopheles mosquitoes. Propanoic pathways are enriched in the poorly-attractive participants compared to those found to be highly-attractive. CONCLUSIONS: Our findings suggest that variation in attractiveness of people to mosquitoes is related to the composition of the skin microbiota, knowledge that could improve odour-baited traps or other next generation vector control tools.

Extending the post-thaw viability of cryoprecipitate.

BACKGROUND: Cryoprecipitate has a short post-thaw expiry time of 6 h. The aim of this study was to assess the stability and function of cryoprecipitate components (FVIII, fibrinogen, vWF, and FXIII) and cryoprecipitate sterility up to 120 h post-thawing when stored at two temperatures (2-6°C and room temperature [20-24°C]). METHODS AND MATERIALS: Twenty batches (110 individual units) of time-expired, thawed cryoprecipitate were collected. Units were sampled at the 6-h expiration mark and then stored at 2-6°C or room temperature (RT). They were resampled every 24 h for 120 h. One unit from each batch was sent for sterility testing at 120 h. Samples had FVIII (one stage and chromogenic), fibrinogen, FXIII, vWFag, and vWF:RCo assays performed in batches. Rotational thromboelastometry (ROTEM) was also performed. RESULTS: FVIII levels declined significantly at 120 h post-thawing at both RT and 2-6°C, but still met international standards for FVIII content. Fibrinogen, vWF antigen, and FXIII levels reduced minimally over 120 h and always met international standard requirements when stored at either temperature. ROTEM analysis demonstrated that fibrinogen function was not compromised at 120 h post-thawing under both storage conditions. vWF:RCo levels declined significantly over 120 h at both storage temperatures. No bacterial contamination was detected in 20 units of cryoprecipitate following storage for 120 h post-thawing. CONCLUSION: These results demonstrate that extension of the storage time of thawed cryoprecipitate to 120 h, stored at either 2-6°C or RT, is feasible while still maintaining required FVIII, fibrinogen, and vWFag levels. Storage at 2-6°C has the advantage of reduced risk of potential bacterial contamination.

Resummed Differential Cross Sections for Top-Quark Pairs at the LHC.

We present state of the art resummation predictions for differential cross sections in top-quark pair production at the LHC. They are derived from a formalism which allows the simultaneous resummation of both soft and small-mass logarithms, which endanger the convergence of fixed-order perturbative series in the boosted regime, where the partonic center-of-mass energy is much larger than the mass to the top quark. We combine such a double resummation at next-to-next-to-leading logarithmic^{'} (NNLL^{'}) accuracy with standard soft-gluon resummation at next-to-next-to-leading logarithmic accuracy and with next-to-leading-order calculations, so that our results are applicable throughout the whole phase space. We find that the resummation effects on the differential distributions are significant, bringing theoretical predictions into better agreement with experimental data compared to fixed-order calculations. Moreover, such effects are not well described by the next-to-next-to-leading-order approximation of the resummation formula, especially in the high-energy tails of the distributions, highlighting the importance of all-orders resummation in dedicated studies of boosted top production.

What might working from home mean for the geography of work and commuting in the Greater Golden Horseshoe, Canada?

The Covid-19 pandemic has highlighted the precarity of urban society, illustrating both opportunities and challenges. Teleworking rates increased dramatically during the pandemic and may be sustained over the long term. For transportation planners, these changes belie the broader questions of how the geography of work and commuting will change based on pandemic-induced shifts in teleworking and what this will mean for society and policymaking. This study focuses on these questions by using survey data (n = 2580) gathered in the autumn of 2021 to explore the geography of current and prospective telework. The study focuses on the Greater Golden Horseshoe, the mega-region in Southern Ontario, representing a fifth of Canadians. Survey data document telework practices before and during the pandemic, including prospective future telework practices. Inferential models are used to develop working-from-home scenarios which are allocated spatially based on respondents' locations of work and residence. Findings indicate that telework appears to be poised to increase most relative to pre-pandemic levels around downtown Toronto based on locations of work, but increases in teleworking are more dispersed based on employees' locations of residence. Contrary to expectations by many, teleworking is not significantly linked to home-work disconnect - suggesting that telework is poised to weaken the commute-housing trade-off embedded in bid rent theory. Together, these results portend a poor outlook for downtown urban agglomeration economies but also more nuanced impacts than simply inducing sprawl.

Effect of varying the concentrations of carbohydrate and milk protein in rehydration solutions ingested after exercise in the heat.

The present study investigated the relationship between the milk protein content of a rehydration solution and fluid balance after exercise-induced dehydration. On three occasions, eight healthy males were dehydrated to an identical degree of body mass loss (BML, approximately 1·8%) by intermittent cycling in the heat, rehydrating with 150% of their BML over 1 h with either a 60 g/l carbohydrate solution (C), a 40 g/l carbohydrate, 20 g/l milk protein solution (CP20) or a 20 g/l carbohydrate, 40 g/l milk protein solution (CP40). Urine samples were collected pre-exercise, post-exercise, post-rehydration and for a further 4 h. Subjects produced less urine after ingesting the CP20 or CP40 drink compared with the C drink (P<0·01), and at the end of the study, more of the CP20 (59 (SD 12)%) and CP40 (64 (SD 6)%) drinks had been retained compared with the C drink (46 (SD 9)%) (P<0·01). At the end of the study, whole-body net fluid balance was more negative for trial C (- 470 (SD 154) ml) compared with both trials CP20 (- 181 (SD 280) ml) and CP40 (2107 (SD 126) ml) (P<0·01). At 2 and 3 h after drink ingestion, urine osmolality was greater for trials CP20 and CP40 compared with trial C (P<0·05). The present study further demonstrates that after exercise-induced dehydration, a carbohydrate--milk protein solution is better retained than a carbohydrate solution. The results also suggest that high concentrations of milk protein are not more beneficial in terms of fluid retention than low concentrations of milk protein following exercise-induced dehydration.

Monitoring mobility in older adults using a Global Positioning System (GPS) smartwatch and accelerometer: A validation study.

There is growing interest in identifying valid and reliable methods for detecting early mobility limitations in aging populations. A multi-sensor approach that combines accelerometry with Global Positioning System (GPS) devices could provide valuable insights into late-life mobility decline; however, this innovative approach requires more investigation. We conducted a series of two experiments with 25 older participants (66.2±8.5 years) to determine the validity of a GPS enabled smartwatch (TicWatch S2 and Pro 3 Ultra GPS) and separate accelerometer (ActiGraph wGT3X-BT) to collect movement, navigation and body posture data relevant to mobility. In experiment 1, participants wore the TicWatchS2 and ActiGraph simultaneously on the wrist for 3 days. In experiment 2, participants wore the TicWatch Pro 2 Ultra GPS on the wrist and ActiGraph on the thigh for 3 days. In both experiments participants also carried a Qstarz data logger for trips outside the home. The TicWatch Pro 3 Ultra GPS performed better than the S2 model and was similar to the Qstarz in all tested trip-related measures, and it was able to estimate both passive and active trip modes. Both models showed similar results to the gold standard Qstarz in life-space-related measures. The TicWatch S2 demonstrated good to excellent overall agreement with the ActiGraph algorithms for the time spent in sedentary and non-sedentary activities, with 84% and 87% agreement rates, respectively. Under controlled conditions, the TicWatch Pro 3 Ultra GPS consistently measured step count in line with the participants' self-reported data, with a bias of 0.4 steps. The thigh-worn ActiGraph algorithm accurately classified sitting and lying postures (97%) and standing postures (90%). Our multi-sensor approach to monitoring mobility has the potential to capture both accelerometer-derived movement data and trip/life-space data only available through GPS. In this study, we found that the TicWatch models were valid devices for capturing GPS and raw accelerometer data, making them useful tools for assessing real-life mobility in older adults.

Child pedestrian injuries and urban change.

BACKGROUND: The health impacts of rapid changes in urban environments due to economic growth and/or retraction are not widely known. This study looks at the effects of urban change on the risk of child pedestrian injury in Edmonton, Alberta, a city that has experienced large economic and population growth following the expansion of the oil and gas industry in Canada. METHODS: A longitudinal ecological study design was used to model the relationships between several built and social environmental variables and the risk of child pedestrian injury and severe child pedestrian injury between 1996 and 2007. RESULTS: The incidence of child pedestrian injury was stable, but the incidence of severe injury increased over the study period. Areas with higher proportions of families on low incomes had higher injury incidence. While new residential development is associated with a lower incidence of injury in most areas, in poor areas, new residential development is associated with a higher incidence, even after controlling for urban planning features and traffic intensity. CONCLUSION: While suburban areas have a lower incidence of child pedestrian injury, residential development in poorer areas is associated with a higher child pedestrian injury risk. Child pedestrians may be less able to adapt to changes in the urban environment due to rapid growth and increasing income, and as a result, may be at greater risk of injury.

Impact of COVID-19 on mobility and participation of older adults living in Hamilton, Ontario, Canada: a multimethod cohort design protocol.

INTRODUCTION: The novel COVID-19 required many countries to impose public health measures that likely impacted the participation and mobility of community-dwelling older adults. This protocol details a multimethod cohort design undertaken to describe short-term and medium-term changes to the mobility and participation of older Canadians living in the community rather than retirement facilities during the COVID-19 pandemic. METHODS AND ANALYSIS: A longitudinal telephone (or online)-administered survey is being conducted with a random sample of older adults living within 20 km of McMaster University, Hamilton, Ontario, Canada, identified from census dissemination areas. Baseline data collection of community-dwelling older adults aged 65 years and over began in May 2020 with follow-ups at 3, 6, 9 and 12 months. The Late-Life Function and Disability Instrument and global rating of change anchors are the primary outcomes of interest. A subsample of respondents will participate in open-ended, semistructured interviews conducted over the telephone or through video-conference, to explore participants' lived experiences with respect to their mobility and participation during the pandemic. Descriptive statistics and quantitative approaches will be used to determine changes in mobility and social and personal participation, and associated personal and environmental factors. For the interviews, qualitative data will be analysed using descriptive phenomenology. ETHICS AND DISSEMINATION: Approval was obtained from the Hamilton Integrated Research Ethics Board of McMaster University (2020-10814-GRA). This study may inform the design of programmes that can support community-dwelling older adults during and after the COVID-19 pandemic. Findings will be disseminated through peer-reviewed publications and conferences focused on ageing.

A Web-Delivered Acceptance and Commitment Therapy Intervention With Email Reminders to Enhance Subjective Well-Being and Encourage Engagement With Lifestyle Behavior Change in Health Care Staff: Randomized Cluster Feasibility Stud.

BACKGROUND: Poor mental health and emotional well-being can negatively impact ability to engage in healthy lifestyle behavior change. Health care staff have higher rates of sickness and absence than other public sector staff, which has implications at both individual and societal levels. Individual efforts to self-manage health and well-being which add to the UK mental health prevention agenda need to be supported. OBJECTIVE: The objective of this study was to establish the feasibility and acceptability of the inclusion of a self-guided, automated, web-based acceptance and commitment therapy intervention in an existing health promotion program, to improve subjective well-being and encourage engagement with lifestyle behavior change. METHODS: For this 12-week, 4-armed, randomized controlled cluster feasibility study, we recruited participants offline and randomly allocated them to 1 of 3 intervention arms or control (no well-being intervention) using an automated web-based allocation procedure. Eligibility criteria were current health care staff in 1 Welsh health board, age≥18 years, ability to read English, and ability to provide consent. The primary researcher was blinded to cluster allocation. Feasibility outcomes were randomization procedure, acceptance of intervention, and adherence to and engagement with the wider program. We evaluated health and well-being data via self-assessment at 2 time points, registration and postintervention, using the 14-item Warwick-Edinburgh Mental Well-Being Scale, the 4-item Patient Health Questionnaire, and the 7-item Acceptance and Action Questionnaire-Revised. RESULTS: Of 124 participants who provided consent and were randomly allocated, 103 completed full registration and engaged with the program. Most participants (76/103) enrolled in at least one health behavior change module, and 43% (41/96) of those randomly allocated to an intervention arm enrolled in the well-being module. Adherence and engagement was low (7/103, 6.8%), but qualitative feedback was positive. CONCLUSIONS: The procedure and randomization process proved feasible, and the addition of the well-being module proved acceptable to health care staff. However, participant engagement was limited, and no one completed the full 12-week program. User feedback should be used to develop the intervention to address poor engagement. Effectiveness should then be evaluated in a full-scale randomized controlled trial, which would be feasible with additional recruitment. TRIAL REGISTRATION: International Standard Randomised Controlled Trial Number (ISRCTN) 50074817; http://www.isrctn.com/ISRCTN50074817.

Separating the effects of climate, bycatch, predation and harvesting on titi (Ardenna grisea) population dynamics in New Zealand: A model-based assessment.

A suite of factors may have contributed to declines in the titi (sooty shearwater; Ardenna grisea) population in the New Zealand region since at least the 1960s. Recent estimation of the magnitude of most sources of non-natural mortality has presented the opportunity to quantitatively assess the relative importance of these factors. We fit a range of population dynamics models to a time-series of relative abundance data from 1976 until 2005, with the various sources of mortality being modelled at the appropriate part of the life-cycle. We present estimates of effects obtained from the best-fitting model and using model averaging. The best-fitting models explained much of the variation in the abundance index when survival and fecundity were linked to the Southern Oscillation Index, with strong decreases in adult survival, juvenile survival and fecundity being related to El Niño-Southern Oscillation (ENSO) events. Predation by introduced animals, harvesting by humans, and bycatch in fisheries also appear to have contributed to the population decline. It is envisioned that the best-fitting models will form the basis for quantitative assessments of competing management strategies. Our analysis suggests that sustainability of the New Zealand titi population will be most influenced by climate, in particular by how climate change will affect the frequency and intensity of ENSO events in the future. Removal of the effects of both depredation by introduced predators and harvesting by humans is likely to have fewer benefits for the population than alleviating climate effects.

Changes in head and neck position have a greater effect on elbow joint position sense in people with whiplash-associated disorders.

BACKGROUND: It has been shown that perception of elbow joint position is affected by changes in head and neck position. Further, people with whiplash-associated disorders (WAD) present with deficits in upper limb coordination and movement. OBJECTIVES: This study is aimed to determine whether the effect of changes in head position on elbow joint position error (JPE) is more pronounced in people with WAD, and to determine whether this is related to the participant's pain and anxiety levels. METHODS: Nine people with chronic and disabling WAD and 11 healthy people participated in this experiment. The ability to reproduce a position at the elbow joint was assessed after changes in the position of the head and neck to 30 degrees , and with the head in the midline. Pain was monitored in WAD participants. RESULTS: Absolute elbow JPE with the head in neutral was not different between WAD and control participants (P=0.5). Changes in the head and neck position increased absolute elbow JPE in the WAD group (P<0.05), but did not affect elbow JPE in the control group (P=0.4). There was a connection between pain during testing and the effect of changes in head position on elbow JPE (P<0.05). DISCUSSION: Elbow JPE is affected by movement of the head and neck, with smaller angles of neck rotation in people with WAD than in healthy individuals. This observation may explain deficits in upper limb coordination in people with WAD, which may be due to the presence of pain or reduced range of motion in this population.

Barriers to Walking: An Investigation of Adults in Hamilton (Ontario, Canada).

This study investigates perceived barriers to walking using data collected from 179 randomly-selected adults between the ages of 18 and 92 in Hamilton, Ontario, Canada. A survey (Hamilton Active Living Study) asked questions about socio-demographics, walking, and barriers to walking. A series of binary logit models are estimated for twenty potential barriers to walking. The results demonstrate that different barriers are associated with different sub-groups of the population. Females, senior citizens, and those with a higher body mass index identify the most barriers to walking, while young adults, parents, driver's license owners, and bus pass owners identify the fewest barriers. Understanding who is affected by perceived barriers can help policy makers and health promotion agencies target sub-groups of the population in an effort to increase walking.

Effect of beta-cyclodextrin in improving the correlation between lycopene concentration and ORAC values.

Lycopene, a lipophilic antioxidant, plays a crucial role in biological systems. It may play an important role in human biological systems by providing protection against cardiovascular disease and some cancers and by boosting the immune system. The oxygen radical absorbance capacity (ORAC) has been validated as an index of antioxidant activity for many hydrophilic antioxidants but not for lycopene. This study validates the ORAC assay for different concentrations of lycopene in the presence of beta-cyclodextrin, a water-solubility enhancer. Lyc-O-Mato 6% extract was used as a source of lycopene for these experiments. Lycopene was extracted according to a standard spectrophotometric assay procedure in the presence of beta-cyclodextrin at concentrations of 0, 0.4, 0.8, and 1.6%, and the antioxidant activity of lycopene was measured with the ORAC assay. Experiments were conducted in quadruplicate and statistical pooled correlations analyzed. Statistical analysis showed a very high correlation (R2 = 0.99) between ORAC and ascorbic acid concentrations, validating this method. Lycopene concentration correlated poorly with ORAC (R2 = 0.33) in the absence of beta-cyclodextrin. Correlations improved with increasing levels of beta-cyclodextrin (R2 = 0.58 and 0.91 for 0.4 and 0.8% beta-cyclodextrin, respectively). A very high beta-cyclodextrin concentration (1.6%) decreased the correlation between ORAC and lycopene concentration. Inclusion of beta-cyclodextrin in the ORAC assay improves correlation between ORAC and lycopene concentration, thus expanding the scope of the ORAC assay to include an additional fat-soluble antioxidant.

Durations and domains of daily aerobic activity: evidence from the 2010 Canadian time-use survey.

BACKGROUND: This study employs national time-diary data to evaluate how much aerobic activity Canadians engage in on a daily basis, how that activity is apportioned by activity domain, and how subgroups within the population vary in their aerobic attainment. METHODS: The study employs time-use data from the 2010 General Social Survey of Canada, for 15,390 respondents aged 15 and older. To estimate effort levels, the authors harmonized survey codes with those in the Compendium of Physical Activities. Aerobic activity was defined as moderate or vigorous effort at 3.5 Metabolic Equivalent of Task (MET) or higher. RESULTS: Among the 4 activity domains, aerobic participation is highest in leisure activities, followed by chores, paid work, and active transportation (AT). Only a minority (42%) of respondents recorded at least 20 mins/day of aerobic activity. Aerobic totals were particularly low for women and those in poor or fair health, and low for students, 15- to 24-year-olds, and those residing in Quebec, Ontario, and larger cities. CONCLUSIONS: The majority of Canadian adults are failing to meet recommended aerobic activity levels. However, there is considerable opportunity to increase aerobic participation for some groups, particularly women and young adults, especially in the leisure and AT domains.

A geography of moral hazard: sources and sinks of motor-vehicle commuting externalities.

Motor-vehicles are responsible for harms to health that are not directly experienced by individual drivers - such as air pollution and risk of injury to pedestrians. In addition to their direct effects on health, these harms also represent a moral hazard since drivers are not required to consider their effects as part of their decision to drive. We describe an approach for estimating sources of motor-vehicle commuter externalities as a means of understanding the geography of moral hazard, and in particular, the spatial displacement of negative health externalities associated with motor-vehicle commuting. This approach models motor-vehicle commuter traffic flow by trip origin for small geographic areas within the City of Toronto, Ontario. We find that most health-related externalities associated with motor-vehicle commuters are not locally generated, with a large share coming from outside Toronto. Low income is associated with externalities originating outside the municipal boundary, but not with locally sourced externalities. We discuss the impact of geographical moral hazard on the agency of citizens as well as policy options aimed at addressing motor-vehicle externalities.

The effects of local and non-local traffic on child pedestrian safety: a spatial displacement of risk.

In most places, motor-vehicle traffic volume is associated with increased risk of child pedestrian injury; however, the burden of risk is geographically complex. In some neighbourhoods, proportionally fewer drivers may be local, meaning that the moral and practical responsibility of risk to children is displaced from one place (e.g., the suburbs) to another (e.g., downtown). Using the City of Toronto, Canada, as a case study, this research asks two related questions: 1) what is the variation in traffic volume by neighbourhood of origin and socioeconomic status and 2) what is the relationship between the geographical origin of traffic and the risk of collisions involving child pedestrians and motor-vehicles? We find that low-income downtown neighbourhoods have the highest proportion of non-local traffic. We also find that while higher local traffic activity is associated with lower risk of collision, higher flow-through traffic activity (excluding traffic from major thoroughfares) is associated with higher risk of collision. We interpret the former as very likely a proxy of parents' frequency of chauffeuring children to school, and the latter an illustration of the spatial displacement of risk between Toronto neighbourhoods. Our results suggest that more attention needs to be paid to account for the externalization of harm experienced by children, particularly in low-income downtown neighbourhoods.

Altering school attendance times to prevent child pedestrian injuries.

OBJECTIVES: The purpose of this research was to determine whether modifying school start time schedules can be used to reduce children's exposure to traffic on their morning walks to school. METHODS: We use models of pedestrian and motor vehicle commuting to estimate the frequency of encounters between child pedestrians and motor vehicles at intersections throughout the City of Hamilton, Ontario, Canada. We use a simple heuristic to identify the school-specific start times that would most reduce the local frequency of encounters between motor vehicles and pedestrians. RESULTS: Our analysis suggests that it may be possible to achieve an almost 15 percent reduction in the total number of encounters between child pedestrians and motor vehicles during the morning commute by staggering school start times such that the periods of high pedestrian activity are temporally staggered from periods of high motor vehicle activity. Our analysis suggests that small changes in school start times could be sufficient to see noteworthy reductions in pedestrian exposure to traffic. CONCLUSIONS: Changing school times may be an effective, inexpensive, and practical tool for reducing child pedestrian injuries in urban environments. Enhanced transportation models and community-based interventions are natural next steps for exploring the use of school-specific scheduling to reduce the risk of child pedestrian injury. Further research is required to validate our models before this analysis should be used by policy makers.

Walking for transport versus recreation: a comparison of participants, timing, and locations.

BACKGROUND: Walking is the most common physical activity for adults with important implications for urban planning and public health. Recreational walking has received considerably more attention than walking for transport, and differences between them remain poorly understood. METHODS: Using time-use data collected from 1971 randomly-chosen adults in Halifax, Canada, we identified walking for transport and walking for recreation events, and then computed participation rates, occurrences, mean event durations, and total daily durations in order to examine the participants and timing, while the locations were examined using origin-destination matrices. We compared differences using McNemar's test for participation rates, Wilcoxon test for occurrences and durations, and Chi-Square test for locations. RESULTS: Results illustrate many significant differences between the 2 types of walking, related to participants, timing, and locations. For example, results indicate a daily average of 3.1 walking for transport events, each lasting 8 minutes on average, compared with 1.4 recreational walking events lasting 39 minutes on average. Results also indicate more than two-thirds of recreational walks are home-based, compared with less than one-fifth of transport walks. CONCLUSIONS: This research highlights the importance of both types of walking, while also casting suspicion on the traditional home-based paradigm used to measure "walkability."

Mapping commuter cycling risk in urban areas.

Cycling is becoming an increasingly important transportation option for commuters. Cycling offers exercise opportunities and reduces the burden of motor vehicle travel on society. Mapping the risk of collision between cyclists and motor vehicles in urban areas is important to understanding safe cyclist route opportunities, making informed transportation planning decisions, and exploring patterns of injury epidemiology. To date, many geographic analyses and representations of cyclist risk have not taken the concept of exposure into account. Instead, risk is either expressed as a rate per capita, or as a count of events. Using data associated with the City of Hamilton, Canada, we illustrate a method for mapping commuter cyclist collision risk per distance travelled. This measure can be used to more realistically represent the underlying geography of cycling risk, and provide more geographically and empirically meaningful information to those interested in understanding how cycling safety varies over space.