Publications by andrew
Hazardous and Benign Space Objects: Getting the Data
The recent story about a skydiver nearly being hit by falling meteor got me thinking about all the pieces of rock floating around in near-Earth space. Despite the fact that the supposed meteor was probably just a chunk of rock mistakenly packed in with a parachute, the fact that something like that could actually happen is quite intriguing. And n...
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Comrades Marathon: Negative Splits and Cheating
With this year’s Comrades Marathon just less than a month away, I was reminded of a story from earlier in the year. Mark Dowdeswell, a statistician at Wits University, found evidence of cheating by some middle and back of the pack Comrades runners. He identified a group of 20 athletes who had suspicious negative splits: they ran much faster in ...
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Hazardous and Benign Space Objects: Solving Kepler’s Equation
Following on from my previous post about Near Earth Objects, today we are going to solve Kepler’s Equation to find the eccentric anomaly, which is the next step towards plotting the positions of these NEOs relative to Earth. The Eccentric, True and Mean Anomalies The relationship between the eccentric and true anomalies are depicted in the figu...
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Comrades Marathon Negative Splits: The Plot Thickens
I have been thinking a little more about those mysterious negative splits. Not too surprisingly, this thinking happened while I was out running along the Durban beachfront this morning. Let’s have a look at the ten most extreme negative splits from Comrades Marathon 2013: > split.ratio.2013 = subset(split.ratio, year == 2013) > # > split.ratio....
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Hazardous and Benign Space Objects: Orbits in the Solar-Ecliptic Reference Frame
In two previous posts in this series I have wrangled NEO orbital data into R and then solved Kepler’s Equation to get the eccentric anomaly for each NEO. The final stage in the visualisation of the NEO orbits will be the transformation of locations from the respective orbital planes into a single reference frame. Reference Frame The heliocentri...
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Race Statistics for Comrades Marathon Novice Runners
Most novice Comrades Marathon runners finish the race on their first attempt and the majority of them walk (shuffle, crawl?) away with Bronze medals. What is a Novice? To paraphrase the dictionary, a novice is “a person who is new to or inexperienced in the circumstances in which he or she is placed; a beginner”. In the context of the Comrade...
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Bayesian nonparametric weighted sampling inference
Yajuan Si, Natesh Pillai, and I write: It has historically been a challenge to perform Bayesian inference in a design-based survey context. The present paper develops a Bayesian model for sampling inference using inverse-probability weights. We use a hierarchical approach in which we model the distribution of the weights of the nonsampled units i...
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Identifying pathways for managing multiple disturbances to limit plant invasions
Andrew Tanentzap, William Lee, Adrian Monks, Kate Ladley, Peter Johnson, Geoffrey Rogers, Joy Comrie, Dean Clarke, and Ella Hayman write: We tested a multivariate hypothesis about the causal mechanisms underlying plant invasions in an ephemeral wetland in South Island, New Zealand to inform management of this biodiverse but globally imperilled ha...
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Concatenating a list of data frames
It’s something that I do surprisingly often: concatenating a list of data frames into a single (possibly quite enormous) data frame. Until now my naive solution worked pretty well. However, today I needed to deal with a list of over 6 million elements. The result was hours of page thrashing before my R session finally surrendered. I suppose I s...
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Twins, Tripods and Phantoms at the Comrades Marathon
Having picked up a viral infection days before this year’s Comrades Marathon, on 1 June I was left with time on my hands and somewhat desperate for any distraction. So I spent some time looking at my archive of Comrades data and considering some new questions. For example, what are the chances of two runners passing through halfway and the fini...
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