You can read my "farewell lecture" (September, 2017) at my blog

To contact me quickly, try email (surname at math dot leidenuniv dot nl), or mobile phone. Click here for my postal and visiting addresses, office and mobile phone numbers, email addresses, and further contact possibilities.

Foraging for wild mushrooms.

The intersection axiom of conditional independence.

Dutch new herring, correlation vs causation, and scientific integrity.

26 August, 2015. They did it at last! A first reaction. What did they do, exactly, and what was my (modest) scientific
contribution.

Illustrations: Figure 7 from "Bertlmann's socks and the nature of
reality", Bell (1981); and the set-up in Delft, 2015.

See "Bell games" for a comparison of the standard Bell experiment
and the Delft "event-ready detectors" version built on top of entanglement swapping.

I was asked by defense lawyers working on behalf of Ben Geen,
to analyse statistical data of
occurrence of respiratory arrest in accident and emergency at numerous
UK hospitals (draft R html notebook,
draft report). After I had done my statistical work, I dug more deeply into
other aspects of the case. The more I discovered, the more I was shocked that
this case was a carbon copy of our own (Netherlands) case of Lucia de Berk.
However there are three important differences. (1) The UK media did an even more
perfect hatchet job on him than the Dutch media did on Lucia. (2) The Criminal Cases
Review Commission is understaffed and underfunded, and takes a formalistic (legalist)
view: give us a "new legal fact" or we will do nothing. (3) There is no Metta de Noo:
no medical whistleblower. In the Lucia case, Metta de Noo fought for 7 years to get
Lucia the fair (re-) trial which Lucia deserved. Metta is a senior medical expert,
well connected in society, and she had inside information about the case.
In the Lucia case, what was needed (and finally happened at the re-trial in Arnhem,
2009--2010) was an independent and thorough re-appraisal of
existing (medical) evidence.

Ben has by now sat out about 12 years of his 30 year sentence.
Because he claims to be innocent
he is denied any "good prisoner" benefits and
will also never get parole or early release.
A small supporters' group set up a website Justice for Ben Geen.

Some UK journalists, at "The Times" no less,
briefly showed some interest:
Nurse 'was victim of Shipman hysteria' But recently his case is forgotten again.

A historical document: statement by Haga-Hospital, 2010, regarding the acquittal of Lucia de Berk: English translation, original.

Four days after the TEDx event, I saw the movie Lucia de B. on its premiere night in Amsterdam. Here is my personal film review: Splendid acting, very moving, beautifully told human story, centering around Lucia herself. Despite compression of the story line and focus on Lucia's personal experiences, it still contained such key features as: the close personal links between key people from hospital, justice and experts (image right); the mental illness and mental breakdown of the chief-paediatrician at JKZ ... There was a vain and ambitious hospital director. A bad statistician. Real life heroine Metta de Noo and hero Ton Derksen were concentrated in the film into the imaginary person of one imaginary whistleblower at the last place you might expect to find them: in the Public Prosecution service. But on the other hand: it wasn't black and white. There were good medics and bad medics, good nurses and bad nurses, good cops and bad cops ... Apparently, even some people in the Public Prosecution service found the witch hunt deeply disturbing.

For more (much, much more) on the Lucia case, see several more items below, as well as yet more items from past versions of my home-page: writings on Lucia.

Some years ago I offered a prize for the person who remasters the logo of the VVS: the Dutch statistical society (top image) in the most beautiful postscript. An exercise in curve fitting with splines, perhaps? Better still would be a mathematical/statistical story of the curves themselves, providing an elegant parametric family which reproduces the whole logo. Finally I decided to do it myself, and I think I am getting close with this perspective image of some very simple 3-dimensional curves, with indeed a statistical story behind them (bottom). The R script which draws this logo can be found here. It should generate a rotatable 3-d image...

See the slides of my Amst-R-dam R users group meetup 2011 (updated 2012) talk R-fun: part 1, the VVS logo in R; part 2, R on an iDevice. For some old news on "R on an iDevice" see the 2014 talk R on an iDevice, given at a Data Science NL meetup.

For more R fun: I am nowadays an enthusiastic user of RStudio and RPubs. You can find all kinds of R work by me at my RPubs site.

VVS stands for "Vereniging voor Statistiek". SMS stands for "Section Mathematical Statistics". The VVS also has an OR section, hence the common alternative name VVS-OR. And nowadays the society has a nice new logo, though it doesn't look to me so much like anything to do with statistics

I must admit to getting a lot of fun (and scientific stimulation) from interacting with Bell-deniers. More generally I consider this an important part of science-outreach: how can we explain Bell's theorem to the general public? Well a good start is to try to understand the mentality of very smart and well-educated people who believe that Bell made some fundamental but simple mistake, that they have exposed that mistake, and that there is an establishment conspiracy to suppress their findings. I wrote a tutorial paper intended to clarify the situation around the Joy Christian model. To my surprise it was *rejected* by arXiv.org on the grounds (a) that it was tutorial in nature, not scientific and (b) that it was personal, not scientific. I therefore joined the crackpots by posting it on viXra.org where it drew (of course) fierce (but IMHO completely unscientific) criticism. Does Geometric Algebra provide a loophole to Bellâ€™s Theorem? These activities also led in (2015) to short papers in the Springer journal IJTP (International Journal of Theoretical Physics) and the Elsevier journal RinP (Results in Physics), refuting results in papers by J. Christian and by H. Geurdes which had appeared in those journals in the same year. I hope someone finds them useful. My "victims" were not amused, I'm sorry for that. I analyse and criticise their work, not their persons.

**Spring 2016**

Master's level (or advanced Bachelor's)

The master specialization Statistical
Science for the Life and Behavioural Sciences is a collaboration of our group with others in biomedical statistics, biostatistics, and psychometrics.

Here you can find links to various courses I have given in the past, in particular quantum statistics, statistics for astronomers, HOVO courses (adult education courses, in Dutch) on use and abuse of statistics, forensic science (Hovo-criminalistiek-statistiek-1, Hovo-criminalistiek-statistiek-2, Hovo-criminalistiek-statistiek-3).

WARNING: Richard P. Feynmann said that attempting to understand quantum mechanics causes you to fall into a black hole, never to be heard from again

The past is particles, the future is a wave

During the academic year 2010-2011 I was

Stimulated by media interest in the Geraerts-Merckelbach controversy on their "Memory" paper, I studied the published summary statistics in this paper using the same techniques as Simonsohn used for Smeesters, and found quite clear statistical evidence for "too good to be true". Without experimental protocols written up prior to the experiment, original data-sets, and laboratory log books detailing all the data selection and manipulation steps which resulted in the final data-set on which the summary statistics in the paper are based, one can only guess how these patterns arose. It certainly need not be fraud (fraud requires active intention to deceive).

R-code for experiment with Simonsohn's fraud test (new version)

Histogram of p-values of an honest researcher

Histogram of p-values of a dishonest researcher

You can continue reading here

Biography and more ...

First Leiden inaugural lecture

Just for fun: things you wish your computer had (including the classic clippy's suicide note)

A few years ago I discovered the enormous disussion on the **Monty Hall (three doors) problem** on wikipedia.
My published writings on the subject are, in order of writing (and in order of
insightfulness) an invited contribution to
Springer's International Encyclopaedia of Statistical Science, 2010,
a paper in Statistica Neerlandica, 2011,
and contributions to the peer reviewed internet encyclopedias
citizendium.org and StatProb.com.
In this manuscript you will find
an expanded version the most recent published work, the
StatProb.com
article.

In these works I distinguish between the original, somewhat
ambiguous, real world question about a famous quiz show, and the many
mathematizations of the question which
have been proposed in the literature. Personally I prefer the lesser
known game
theoretic version. For me, the question is not "what is this
probability?" or "what is that probability?", but: "what would you do?"
And to me, the wikipedia controversy around
the Monty Hall problems (concerning whether we should compute a
conditional or unconditional probability of getting the car if we
switch doors) is a warning against solution-driven science.
I want to thank so many wikipedia editors for the inspiration they gave
me.

Suppose the car is hidden behind one of the three
doors by a fair randomization. The contestant chooses Door 1. Monty
Hall, for reasons best known to himself, opens Door 3 revealing a goat.
We know that whatever probability mechanism is used by Monty for this
purpose, the conditional probability that switching will give the car
is at least 1/2. We know that the unconditional probability (ie not
conditioning on the door chosen by the contestant, nor the door opened
by Monty) is 2/3.

Always switching gives the car with unconditional probability 2/3,
always staying gives it with probability 1/3. Nobody in their right
mind could imagine that there could exist some mixed strategy
(sometimes staying, sometimes switching, perhaps with the help of some
randomization device, and all depending on which doors were chosen and
opened) which would give you a better overall (ie unconditional) chance
than 2/3 of getting the car.

This is true, of course. In fact, from the law of total
probability, proving the optimality of (unconditional) 2/3 by always
switching is equivalent to proving that all the six conditional
probabilities of winning by switching, given door chosen and door
opened, are at least 1/2. We can prove the latter using Bayes' theorem,
or, better I think, using Bayes' rule in a smart way. However both
these proofs require some sophistication.

Is there an elementary proof? A short proof using words and ideas, no computations.

Yes there is, and I learnt it from Sasha Gnedin.

However you play there's always a door such that if the car is
there, you'll miss it. Consider first deterministic strategies. We only
need consider two cases: for "always switching" it's the door you
initially chose, and for "sometimes switching" it's a door you won't
switch to if you get the option. (If you never switch there are two
such doors: just choose one). Ordinary readers won't be interested in
randomized strategies but anyone who wants to include these will
understand how to do it (now the door where you'ld certainly miss a car
has to be a random door, determined by the same coin tosses used to
implement the random choices in your own strategy).

Note that the door which has been indicated in this way does not
depend on where
the car is actually hidden or how the host plays: it just depends on
how the player plays. Therefore if the car is initially equally likely
to be behind any of the three doors, we run a 1/3 chance that the car
will be missed because it's behind this door. Therefore the 2/3
success-chance of always switching can't be beaten.

I would call this a proof by coupling.

From Three Doors to Two Envelopes (what will be next? One Coffin, perhaps?). Here is my fourth (still incomplete) draft of the definitive article on the infamous two envelopes problem. The problem which Martin Gardner could not solve, and which many other famous people got wrong. Studied by probabilists, logicians, economists, philosophers. Now studied by me ...

The mathematical heart of all exchange paradoxes is encapsulated in a little theorem which I call my "unified solution". It seems to be new.

The tunnel-vision which characterized Lucia's case was cemented in the two weeks around "the" nine-eleven

The hospital investigators into the crime were the same people earlier treating those patients, and making, as is completely natural, errors of diagnosis or treatment from time to time. The collegiality of the medical community means that mistakes by medical specialists within the Netherlands can hardly be admitted by others inside the same relatively tight, and extremely powerful, community. Highly placed medical authorities had to stand firm by their own previous and now provenly mistaken diagnoses. Others would be loath to criticise a highly regarded colleague's decisions in such a critical case.

In the Netherlands, medical practitioners almost never admit to having made mistakes... consequently, they do not have to insure themselves agaist being sued for malpractice (which is good for their income), and in theory medical treatment should be less expensive than in other countries where lawyers and insurance companies profit from medical missers. However the Dutch arrangement has led to increasing distress among all those "victims" of medical errors, many of whom would probably be satisfied just to have an "accident" admitted! This June 16, a new code of practice has been introduced, by which medical practitioners will in future be able to apologize for errors without thereby admitting legal responsibility. A giant step for the medical profession, though only a very small step for their patients. Better than nothing, or merely a crumb to keep us "consumers" (the ones who pay for health care) quiet?

Many years after judicial authorities apologized personally and publicly, it is still high time to start finding out where avoidable mistakes were made. It is hard to believe that these can only be attributed to police investigation and legal procedures. However that is the implication of the public statement by the board of Lucia's hospital, (unauthorized rough English translation).

**
Statistical ethics of the probiotica trial.
**
This randomized triple-blind clinical trial of probiotics treatment
for patients with predicted severe acute pancreatitis ended in controversy,
when it transpired at the conclusion of the trial in
December 2007, that rather more patients had died on the treatment
arm of the trial than on the control arm.

It seemed strange that the trial had not been terminated at the
interim analysis. The researchers were using a a stopping rule
of S.M. Snapinn, by which the trial would
to be terminated early either if it were almost certain that the
final result would be a significant positive effect of probiotica,
or if it were almost certain that the final result would be insignificant.
Here is a paper by myself, to appear
in *Statistica Neerlandica*,
and, in Dutch, a short article by
probabilist Ronald Meester and microbiologist Pieter ter Steeg which
appeared in the newspaper Trouw and an
open letter
to Meester and ter Steeg
by biostatisticians Hans van Houwelingen and Theo Stijnen.
Also in Dutch there are a series of interviews (early 2008)
on the current affairs chat show
'Pauw and Witteman':
chairman of the hospital board Geert Blijham, 23 January;
patient Jochim Vromans, 24 Jaunary;
probiotics expert Eric Claassen, 25 January;
leader of the research team Hein Gooszen, 14 February.

Later we obtained the data at the time of the interim analysis.
It was given to journalists at a press conference on Feb. 13 2008,
but never released to interested scientists.
It turned out that the probiotica trial was
*not* terminated for futility (following the Snapinn stopping
rule) at the half way interim analysis,
through a mis-reading of output of the SPSS package,
which, without consulting the user,
always reports the *smaller* p-value of the
*two* one-sided Fisher's exact tests for
equality of two binomial probabilities. Proper application of their
own stopping rule would have led to early termination of the trial,
since according to the criteria set in advance,
there was no chance any more that it would result in a positive
result for the probiotica treatment. The trial
was de facto continued because there was a good chance that it
would finally result in a *negative* result for probiotica.
Here are slides
of my talk careless statistics costs lives
on the subject.

**Mathematical Centre (Amsterdam) publications are now available on internet**.
Here are two early works which had quite some impact, including
the reprint of my 1979 PhD thesis:

R.D. Gill (1980),
Censoring
and Stochastic Integrals, MC Tract 124.

R.D. Gill (1983),
The
sieve method as an alternative to dollar-unit
sampling: the mathematical background, Report SN 12

Another useful link is to my Saint Flour lectures on survival analysis.

**Product-integrals** are to
products, as integrals are to sums. Though they have been around for
more than a hundred years, they never became part of the standard
toolbox, possibly because no-one invented the right mathematical symbol
for them. I made a try quite some years ago, though they still have not
caught on yet. With the crucial help of JC Loredo, my efforts resulted
in
prodint.zip, files for getting beautiful \prodi and \Prodi and \PRODI symbols in your LaTeX, and Loredo.ttf,
a TrueType font for ordinary word processing. It is not that difficult
these days to get new fonts into your latex, see for instance TUG's font installation instructions.

(Last updated: 30 January 2019)