Bio

I’m a statistician working at Queensland University of technology on a range of environmental and environmental health problems such as jaguar conservation, reef conservation, and air pollution and its health impacts. In addition, I teach mathematics and statistics to first year science students in the unit SEB113 - Quantitative Methods in Science.

My undergrad was in applied and computational mathematics, focussing on fluid dynamics in my honours year. Over time, I drifted towards Bayesian statistical modelling, where I use semi-parametric regression and hierarchical modelling for spatial, temporal, and spatio-temporal modelling.

Occasionally, I blog about my research and you can find more about my publication history at QUT eprints and Google Scholar. Occasionally I publish useful code, including a package for tidying MCMC output from coda or rjags entitled mmcc.

ACEMS

From 2016 I have been employed as a Postdoctoral Fellow at the QUT node of the ARC Centre of Excellence for Mathematical and Statistical Frontiers, working on a variety of environmental statistics problems such as coral cover in the Great Barrier Reef and jaguar conservation in Peru.

Dengue fever transmission

I am working with colleagues at QUT and QIMR to investigate the spread of Dengue fever.

Coral cover on the Great Barrier Reef

The Monitoring Through Many Eyes project is a collaboration between scientists, data analysts and marine explorers, working together to document, analyse and predict the health of the Great Barrier Reef. The aim is to tap into the power of Citizen Scientists by collating thousands of underwater images take by recreational divers and snorkelers on the Reef each year.

Citation Description
Vercelloni et al. (submitted) Gathering information from experts and citizen scientists in a virtual environment to understand what people believe makes an aesthetically pleasing reef

Jaguar conservation in the Peruvian Amazon

The world needs new ways to do conservation. There is no time for endangered animals and their environments. We need an evidence base to make informed decisions, and we need it now. We are addressing this problem by combining traditional conservation with virtual reality technology, mathematical and statistical modelling, local knowledge and international expertise.

Through our Many Eyes on the Wild program, we aim to facilitate faster, better decisions about management and monitoring. We are developing and using these approaches to help conserve jaguars in the Peruvian Amazon.

Citation Description
Mengersen et al. (2017) Spatial modelling of presence only data with a variety of statistical and machine learning techniques
Bednarz et al. (2016) Using virtual environments to elicit information about ecosystems

Bayesian spike sorting

I am currently working on simulation studies for two papers with a former ACEMS PhD student, Dr Zo? van Havre, where we are looking at finite and infinite mixture modelling methods for classifying action potential data from EEG scans.

Citation Description
van Havre et al. (2017) Overfitted mixtures and Dirichlet process mixtures for spike classification

ILAQH

Between 2010 and 2013 I was a PhD student at the International Laboratory for Air Quality and Health (ILAQH) under the supervision of Professors Lidia Morawska and Kerrie Mengersen and Dr Sama Low Choy.

Between 2013 and 2015 I was employed as a Postdoctoral Fellow at ILAQH to support the research being done across a variety of topics in air quality.

I still collaborate with colleagues at ILAQH on a variety of topics including occupational exposure, child health, atmospheric processes, exposure assessment, and instrumentation.

Air quality

Citation Description
Md Mahmudur Rahman, Yeganeh, et al. (2017) Land use regression modelling with variable selection of NO\(_\mathrm{x}\) and NO\(_2\) concentrations
Md Mahmudur Rahman, Mazaheri, et al. (2017) Bayesian GAMs used to model urban background particle concentrations and the contribution of new particle formation
Salimi et al. (2017) Investigating new particle formation events that occur outside normal conditions
Rivas et al. (2017) Identification of problems with DustTrak performance seen during measurement campaigns
Yeganeh et al. (2017) A variety of models used to estimate air pollution concentrations from satellite imagery
Salonen et al. (2016) A review of endotoxin concentrations in a range of indoor environments around the world
McGarry et al. (2016) Characterisation of air quality in the workplace with multiple instruments
Salthammer et al. (2016) Impact of climate and air pollution on children’s health at school
Faghihi et al. (2015) Generalised Linear Mixed Models for understanding the effects of different surface treatments in a nanomaterial milling process
Salonen, Duchaine, et al. (2015a) A review paper on fungi concentrations in schools around the world
Jayaratne, Clifford, and Morawska (2015) Predictive model for whether or not midday new particle formation events will occur based on morning PM\(_{10}\) and visibility
Wangchuk et al. (2015) Children’s exposure to air pollution in rural Bhutan

Air quality and children’s health

The bulk of my postdoctoral work at ILAQH was related to the UPTECH project. The project seeks to determine the effect of the exposure to airborne nano and ultrafine (UF) particles emitted from motor vehicles on the health of children in schools.

Citation Description
Laiman et al. (submitted) The relationship between indoor and outdoor air quality in primary schools
Ezz et al. (2015) Methods paper for the UPTECH project
Toms et al. (2015) Multinomial regression modelling to look at the relative proportions of various polybrominated diphenyl ethers across classrooms
Salimi et al. (2014) Application of clustering techniques to particle size distribution data to understand common source signatures
Clifford et al. (2014) Mathematical and statistical models for particle deposition inside the lung
Mazaheri et al. (2014) Analysis of inhaled particles in primary school children
Laiman et al. (2014) Bayesian hierarchical models for calculating air exchange rates and particle deposition rates associated with classroom activities
Salonen, Duchaine, et al. (2015b) Concentrations of fungi in primary school classrooms
Salonen et al. (2013) Concentrations of endotoxins in primary school classrooms

PhD Thesis

Thesis outputs

Citation Description
Clifford (2013) Spatio-temporal modelling of ultrafine particle number concentration - Using the Generalised Additive Model to model temporal trends in ultrafine particle number concentration with penalised splines and spatial trends with Gaussian Markov Random fields.
Falk et al. (2015) Review paper on modern statistical methods for analysing spatial data
Clifford, Low Choy, et al. (2013) Spatio-temporal model in INLA of air pollution in Brisbane, Australia
Clifford and Low Choy (2012) A book chapter on various implementations of Bayesian spline regression
Clifford, Mølgaard, et al. (2012) A preprint of an unpublished paper looking into Bayesian GAMs with autocorrelated errors
Clifford, Low Choy, et al. (2011) Using GAMs to model temporal trends and covariate effects for PNC in Helsinki, Finland

Other publications

These papers represent work undertaken during the PhD, typically with other PhD students within ILAQH

Citation Description
Stevanovic et al. (2015) Semi-parametric regression used to model particle losses in aerosol measuring equipment
Mølgaard et al. (2013) Work that came out of a visit to Helsinki, Finland, using Bayesian GAMs with autocorrelated errors to understand air quality in multiple European cities
Salimi et al. (2013) Spatial variation of air quality within primary schools

Conference items

Citation Description
Falcão et al. (2016) Modern statistical techniques for understanding indoor/outdoor relationships in air pollution
Clifford et al. (2015) A missing data model for estimating cigarette exposure from survey data and partially complete blood tests
Mazaheri, Clifford, and Morawska (2015) Comparing two methods of exposure assessment
Rahman et al. (2015) Source characterisation in an urban area
Karunasinghe et al. (2015) Land Use Regression for air pollution
Morawska et al. (2014) Synthesis of indoor air pollution results from UPTECH study
Clifford, Mazaheri, Jayaratne, et al. (2013) Presentation of the work in Clifford et al. (2014)
Buonanno et al. (2013) Comparison of inhaled particle doses for Italian and Australian students
Clifford, Mazaheri, Low Choy, et al. (2012) Identification of subpopulations in epidemiological studies
Clifford, Low Choy, et al. (2012) Poster on spatio-temporal modelling of air quality at ISBA2012
Clifford, Low Choy, et al. (2011) Poster on spatio-temporal modelling of air quality at 8BNP

Education

Since 2013 I have been involved in the development and delivery of SEB113 - Quantitative Methods for Science as part of the ST01 Bachelor of Science course at Queensland University of Technology. The course covers a variety of mathematical and statistical topics taught through scientific case studies and makes use of the R language for all computation.

In 2015, the teaching team was the recipient of the Vice Chancellor’s Performance Award for innovation in redesiging the unit for student success through encouraging engagement with multiple technologies.

Citation Description
Czaplinski et al. (2016) Redesign of a first year unit with blended learning to improve student engagement and success

References

Bednarz, Tomasz, June Kim, Ross Brown, Allan James, Kevin Burrage, Sam Clifford, Jacqueline Davis, et al. 2016. “Virtual Reality for Conservation.” In Proceedings of the 21st International Conference on Web3d Technology, 177–78. ACM. http://dl.acm.org/citation.cfm?id=2945319.

Buonanno, G., M. Mazaheri, F. Fuoco, S. Clifford, A. Russi, L. Morawska, P. Vigo, R. Jayaratne, and A. Viola. 2013. “Alveolar dose comparison of ultrafine particles for Australian and Italian children.” Metrology Association of Australia. https://eprints.qut.edu.au/62902/.

Clifford, S., M. Mazaheri, B. Yeganeh, K. Mengersen, G. Marks, and L. Morawska. 2015. “Uncertainty in Exposure Estimates and Imputation of Missing Aerosol Data in an Epidemiological Study.” Poster – European Aerosol Conference.

Clifford, Sam. 2013. “Spatio-Temporal Modelling of Ultrafine Particle Number Concentration.” Doctoral Thesis, School of Chemistry, Physics; Mechanical Engineering, Queensland University of Technology. https://eprints.qut.edu.au/63528/.

Clifford, Sam, and Sama Low Choy. 2012. “Case Studies in Bayesian Statistical Modelling and Analysis.” In, edited by Clair Alston and Kerrie Mengersen, 197–220. Wiley Series in Probability and Statistics. Wiley. http://au.wiley.com/WileyCDA/WileyTitle/productCd-1119941822.html.

Clifford, Sam, Sama Low Choy, Tareq Hussein, Kerrie Mengersen, and Lidia Morawska. 2011. “Using the Generalised Additive Model to Model the Particle Number Count of Ultrafine Particles.” Atmospheric Environment 45 (32): 5934–45. http://www.sciencedirect.com/science/article/pii/S1352231011004766.

Clifford, Sam, Sama Low Choy, Mandana Mazaheri, Farhad Salimi, Kerrie Mengersen, and Lidia Morawska. 2013. “A Bayesian Spatio-Temporal Model of Panel Design Data: Particle Number Concentration in Brisbane, Australia.” ArXiv, no. 1206.3833 (february). http://arxiv.org/abs/1206.3833.

Clifford, Sam, Sama Low Choy, Kerrie Mengersen, and Lidia Morawska. 2011. “Semi-Parametric Modelling of Ultrafine Particle Number Concentration.” Poster – 8th Workshop on Bayesian Non-parametrics.

———. 2012. “Semi-Parametric Modelling of Ultrafine Particle Number Concentration.” Poster – ISBA World Meeting. https://eprints.qut.edu.au/54100/.

Clifford, Sam, Mandana Mazaheri, E. R. Jayaratne, M. A. Megat Mokhtar, F. Fuoco, G. Buonanno, and L. Morawska. 2013. “Estimation of Inhaled Ultrafine Particle Surface Area Dose in Urban Environments.” Australian Mathematical Society (Australian; New Zealand Industrian; Applied Mathematics).

———. 2014. “Estimation of Inhaled Ultrafine Particle Surface Area Dose in Urban Environments.” ANZIAM Journal 55: C437–C447. http://journal.austms.org.au/ojs/index.php/ANZIAMJ/article/view/7819.

Clifford, Sam, Mandana Mazaheri, Sama Low Choy, Kerrie Mengersen, and Lidia Morawska. 2012. “Analysing the Health Impacts of Air Quality on Children According to a Nonparametric Clustering.” International Society for Indoor Air Quality; Climate.

Clifford, Sam, Bjarke Mølgaard, Jukka Corander, Kaarle Hämeri, Sama Low Choy, Kerrie Mengersen, and Tareq Hussein. 2012. “Bayesian Semi-Parametric Forecasting of Particle Number Concentration: Penalised Splines and Autoregressive Errors.” ArXiv, no. 1207.0558 (september). http://arxiv.org/abs/1207.0558.

Czaplinski, Iwona, Sam Clifford, Ruth Luscombe, and Brett Fyfield. 2016. “A Blended Learning Model for First Year Science Student Engagement with Mathematics and Statistics.” http://eprints.qut.edu.au/96972/.

Ezz, Wafaa Nabil, Mandana Mazaheri, Paul Robinson, Graeme Johnson, Sam Clifford, Congrong He, Lidia Morawska, and Guy B. Marks. 2015. “Ultrafine Particles from Traffic Emissions and Children’s Health.” International Journal of Environmental Research and Public Health 12 (2): 1687–1702. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4344688/.

Faghihi, Ehsan Majd, Darren Martin, Samuel Clifford, Grant Edwards, Congrong He, Christof Asbachc, and Lidia Morawska. 2015. “Are There Generalisable Trends in the Release of Airborne Synthetic Clay Nanoparticles from a Jet Milling Process?” Aerosol and Air Quality Research 15 (2): 365–75. http://www.aaqr.org/Doi.php?id=1_AAQR-14-06-OA-0124&v=15&i=2&m=4&y=2015.

Falcão, L, Sam Clifford, Mandana Mazaheri, David Broday, and Lidia Morawska. 2016. “The Influence of Meteorology of Indoor Pm\(_{2.5}\) Concentration: Application of Advanced Modelling Techniques.”

Falk, M. G., C. L. Alston, C. A. McGrory, S. Clifford, E. A. Heron, D. Leonte, M. Moores, C. D. Walsh, A. N. Pettitt, and K. L. Mengersen. 2015. “Recent Bayesian Approaches for Spatial Analysis of 2-d Images with Application to Environmental Modelling.” Environmental and Ecological Statistics 22 (3): 571–600. https://link.springer.com/article/10.1007%2Fs10651-015-0311-1.

Jayaratne, E. R., S. Clifford, and L. Morawska. 2015. “Atmospheric Visibility and PM10 as Indicators of New Particle Formation in an Urban Environment.” Environmental Science & Technology 49 (21): 12751–7. http://pubs.acs.org/doi/abs/10.1021/acs.est.5b01851.

Karunasinghe, Jayan, Luke Knibbs, Sam Cliford, and Lidia Morawaska. 2015. “Land Use Regression Model for Ultrafine Particles in Brisbane.” Kanazawa, Japan.

Laiman, R., C. He, M. Mazaheri, S. Clifford, F. Salimi, M. A. Megat Moktar L. Crilley, and L. Morawska. submitted. “The Effect of Outdoor Sources on Indoor Particle Concentrations in Primary Schools.” Atmospheric Environment.

Laiman, Rusdin, Congrong He, Sam Clifford, Farhad Salimi, Leigh Crilley, Megat Azman Megat Mokhtar, Mandana Mazaheri, and Lidia Morawska. 2014. “Characteristics of Ultrafine Particle Sources and Deposition Rates in Primary School Classrooms.” Atmospheric Environment 94: 28–35. http://www.sciencedirect.com/science/article/pii/S1352231014003604.

Mazaheri, M., S. Clifford, and L. Morawska. 2015. “Inhaled Particle Surface Area Dose: Stationary Vs Personal Monitoring.” Poster – European Aerosol Conference.

Mazaheri, Mandana, Sam Clifford, Rohan Jayaratne, Megat Azman Megat Mokhtar, Fernanda Fuoco, Giorgio Buonanno, and Lidia Morawska. 2014. “School Children’s Personal Exposure to Ultrafine Particles in the Urban Environment.” Environmental Science and Technology 48 (1): 113–20. http://pubs.acs.org/doi/abs/10.1021/es403721w.

McGarry, Peter, Sam Clifford, Luke D Knibbs, Congrong He, and Lidia Morawska. 2016. “Application of Multi-Metric Approach to Characterization of Particle Emissions from Nanotechnology and Non-Nanotechnology Processes.” Journal of Occupational and Environmental Hygiene 13 (10). Taylor & Francis: D175–D197. http://www.tandfonline.com/doi/full/10.1080/15459624.2016.1200194.

Mengersen, Kerrie, Erin E. Peterson, Samuel Clifford, Nan Ye, June Kim, Tomasz Bednarz, Ross Brown, et al. 2017. “Modelling Imperfect Presence Data Obtained by Citizen Science.” Environmetrics. Wiley, e2446–n/a. http://onlinelibrary.wiley.com/doi/10.1002/env.2446/full.

Morawska, L., M. Mazaheri, S. Clifford, F. Salimi, R. Laiman, and L Crilley. 2014. “Indoor Air Pollution Sources and Exposures in Primary Schools: UPTECH Synthesis .” In Indoor Air. Hong Kong.

Mølgaard, Bjarke, Wolfram Birmili, Sam Clifford, Andreas Massling, Kostas Eleftheriadis, Michael Norman, Stergios Vratolis, et al. 2013. “Evaluation of a Statistical Forecast Model for Size-Fractionated Urban Particle Number Concentrations Using Data from Five European Cities.” Journal of Aerosol Science 66: 96–110. http://www.sciencedirect.com/science/article/pii/S0021850213001833.

Rahman, M. M., M. Mazaheri, S. Clifford, and L. Morawska. 2015. “Characterisation and Sources of Ultrafine Particles in an Inner City Urban Area.” Poster – European Aerosol Conference.

Rahman, Md Mahmudur, Mandana Mazaheri, Sam Clifford, and Lidia Morawska. 2017. “Estimate of Main Local Sources to Ambient Ultrafine Particle Number Concentrations in an Urban Area.” Atmospheric Research 194. Elsevier: 178–89. http://www.sciencedirect.com/science/article/pii/S0169809516303684.

Rahman, Md Mahmudur, Bijan Yeganeh, Sam Clifford, Luke Knibbs, and Lidia Morawska. 2017. “Development of a Land Use Regression Model for Daily NO\(_2\) and NO\(_x\) Concentrations in the Brisbane metropolitan area, Australia.” Environmental Modelling and Software accepted.

Rivas, Ioar, Mandana Mazaheri, Mar Viana, Teresa Moreno, Samuel Clifford, Congrong He, Oliver F Bischof, et al. 2017. “Identification of Technical Problems Affecting Performance of Dusttrak Drx Aerosol Monitors.” Science of The Total Environment 584. Elsevier: 849–55. http://www.sciencedirect.com/science/article/pii/S0048969717301390.

Salimi, F., M. Mazaheri, S. Clifford, L. Crilley, R. Laiman, and L. Morawska. 2013. “Spatial Variation of Particle Number Concentration in School Microscale Environments and Its Impact on Exposure Assessment.” Environmental Science and Technology 47 (10): 5251–8. http://pubs.acs.org/doi/abs/10.1021/es400041r.

Salimi, F., Z. Ristovski, M. Mazaheri, R. Laiman, L. Crilley, C. He, S. Clifford, and L. Morawska. 2014. “Assessment and Application of Clustering Techniques to Atmospheric Particle Number Size Distribution for the Purpose of Source Apportionment.” Atmospheric Chemistry and Physics 14: 15257–81. http://www.atmos-chem-phys.net/14/11883/2014/.

Salimi, Farhad, Md Rahman, Sam Clifford, Zoran Ristovski, Lidia Morawska, and others. 2017. “Nocturnal New Particle Formation Events in Urban Environments.” Atmospheric Chemistry and Physics 17 (1). Copernicus GmbH: 521–30. http://www.atmos-chem-phys.net/17/521/2017/.

Salonen, Heidi, C. Duchaine, M. Mazaheri, S. Clifford, S. Lappalainen, K. Reijula, and L. Morawska. 2015a. “Airborne Viable Fungi in School Environments in Different Climatic Regions - a Review.” Atmospheric Environment 104: 186–94. http://www.sciencedirect.com/science/article/pii/S135223101500014X.

Salonen, Heidi, Caroline Duchaine, Valérie Létourneau, Mandana Mazaheri, Sam Clifford, and Lidia Morawska. 2013. “Endotoxins in Indoor Air and Settled Dust in Primary Schools in Subtropical Climate.” Environmental Science and Technology 47 (17): 9882–90. http://pubs.acs.org/doi/abs/10.1021/es4023706.

Salonen, Heidi, Caroline Duchaine, Valérie Létourneau, Mandana Mazaheri, Sirpa Laitinen, Sam Clifford, Raimo Mikkola, Sanna Lappalainen, Kari Reijula, and Lidia Morawska. 2016. “Endotoxin Levels and Contribution Factors of Endotoxins in Resident, School, and Office Environments — a Review.” Atmospheric Environment 142. Pergamon: 360–69. http://www.sciencedirect.com/science/article/pii/S1352231016306124.

Salonen, Heidi, Caroline Duchaine, Mandana Mazaheri, Sam Clifford, and Lidia Morawska. 2015b. “Airborne Culturable Fungi in Naturally Ventilated Primary School Environments in a Subtropical Climate.” Atmospheric Environment 106: 412–18. http://www.sciencedirect.com/science/article/pii/S1352231014005822.

Salthammer, Tunga, Erik Uhde, Tobias Schripp, Alexandra Schieweck, Lidia Morawska, Mandana Mazaheri, Sam Clifford, et al. 2016. “Children’s Well-Being at Schools: Impact of Climatic Conditions and Air Pollution.” Environment International 94. Pergamon: 196–210. http://www.sciencedirect.com/science/article/pii/S0160412016301829.

Stevanovic, S., B. Miljevic, P. Madl, S. Clifford, and Z. Ristovski. 2015. “Characterisation of a Commercially Available Thermodenuder and Diffusion Drier for Ultrafine Particles Losses.” Aerosol and Air Quality Research 15 (1): 357–63. http://www.aaqr.org/Doi.php?id=30_AAQR-13-12-TN-0355.

Toms, L., M. Mazaheri, S. Brommer, S. Clifford, D. Drage, J. Mueller, P. Thai, S. Harrad, L. Morawska, and F. Harden. 2015. “Brominated Flame Retardants in Primary Schools: Sources and Exposures.” Environmental Research 142: 135–40. http://www.sciencedirect.com/science/article/pii/S0013935115001826.

van Havre, Zoé, Nicole White, Judith Rousseau, Sam Clifford, and Kerrie Mengersen. 2017. “Clustering Action Potential Spikes: Insights on the Use of Overfitted Finite Mixture Models and Dirichlet Process Mixture Models.” Australia and New Zealand Journal of Statistics under review.

Vercelloni, Julie, Sam Clifford, Alan R Pearse, Ross Brown, Allan James, Bryce Christensen, Tomasz Bednarz, et al. submitted. “Understanding Aesthetic Attributes of Coral-Reefs: Using Virtual Reality to Support Conservation of Ecosystem Services.” Conservation Letters.

Wangchuk, T., M. Mazaheri, S. Clifford, M. Dudzinska, C. He, G. Buonanno, and L. Morawska. 2015. “Children’s Personal Exposure to Air Pollution in Rural Villages in Bhutan.” Environmental Research 140: 691–98. http://www.sciencedirect.com/science/article/pii/S0013935115001814.

Yeganeh, Bijan, Michael G Hewson, Samuel Clifford, Luke D Knibbs, and Lidia Morawska. 2017. “A Satellite-Based Model for Estimating Pm 2.5 Concentration in a Sparsely Populated Environment Using Soft Computing Techniques.” Environmental Modelling & Software 88. Elsevier: 84–92. http://www.sciencedirect.com/science/article/pii/S1364815216309483.