Marco Fattore
Where is PyHasse a good tool for? Marco Fattore is answering questions
about his work today and in the past.
Rainer Brüggemann: How did you come into touch with partial order
theory?
Marco Fattore: I got in touch with posets more or less in 2006, by reading a book on
social networks; I was intrigued by the concept, which seemed to me
simple and profound, at the same time. As a physicist, I like abstract
relations, so I began reading something about partial
orders. Moreover, in that period I was looking for new research paths
in applied statistics (I have a position as assistant professor at the
Department of Statistics and Quantitative Methods, at University of
Milano-Bicocca, Italy). Working on the problem of multidimensional
poverty measurement, I had to deal with a lot of socio-economic
datasets composed of ordinal attributes, naturally leading to
posets. Strangely enough, however, almost no mention on posets could
be found in the mainstream data analysis literature. People were
increasingly using multidimensional ordinal data, but poset theory was
not in the toolbox of statisticians. So I had the idea that something
new and interesting could be developed, entering this “empty space”…
Then I met Rainer Bruggemann, in 2007, almost by chance, and then I
discovered that I was not the only to think partial order could be a
fundamental language for modern data analysis… We then began
cooperating, writing papers together, making presentations, organizing
workshops, editing books… and applied poset theory became my research
area.
Rainer Brüggemann: What is your scientific field actually?
Marco Fattore: My field is applied statistics and the treatment of multi-indicator
systems in socio-economics, particularly when ordinal attributes are
involved. Measuring, synthesizing and evaluating quality-of-life, or
poverty, or well-being and many other complex socio-economic
constructs… these are some of the topics I am involved in. But
abstracting from specific issues, the point is that we are
increasingly dealing with multidimensionality and complexity. And when
you have to measure something that you cannot collapse to
unidimensionality, you actually have to compare multidimensionally
something to something else. So posets come into play… The key concept
is that of “incomparability”. In the classical statistical culture,
incomparabilites are an effect of noise and latent unidimensionality
is often assumed. But in fact, socio-economic phenomena are inherently
multidimensional and incomparabilities reflect this irreducible
complexity. We need “formal objects” capable to capture this feature,
i.e. we need posets. It is not just a technical tool; it is primarily
a change of mind.
Rainer Brüggemann: What makes partial order attractive for you -
beside its elegance in algebraic terms?
Marco Fattore: People usually build composite indicators, viewing synthesis as
attribute aggregation. However, the scientific community is realizing
that summing “apples and oranges” often produce unreliable results,
scientifically weak and problematic for decision-making. Moreover,
ordinal scores cannot even be summed… Most research is still devoted
to how to treat ordinal data using tools from Euclidean space theory,
but I think the true challenge is to import the mathematics of order
into data analysis, not to export multidimensional ordinal data to
linear spaces. So, also from a methodological point of view, new
research avenues open, since there is a gap between poset theory as a
branch of discrete mathematics and poset theory as a part of applied
math.
Rainer Brüggemann: What are your plans in the future?
Marco Fattore: Considering my field, I see some challenges for future research and
scientific activity. The measure of inequality is a cornerstone of
socio-economic statistics. Going “beyond GDP”, however, requires to
extend the classical theory of index to multi-indicator systems of
attributes, often ordinal. This requires developing a theory of
functional over posets, something that I began working on, but a lot
is still to be done. Another intriguing issue, is the problem of poset
quantification. A recent fascinating paper by Kevin Knuth investigated
the relationship between partially ordered sets and physical
measurement, leading to a derivation of special relativity from
partial order axioms! The mathematics of posets has surely something
to say on measurement and evaluation, in socio-economics. A third
research field is about building inferential statistics on posets. For
example, when dealing with multidimensional systems of numerical
variables, small fluctuations in variable scores may lead to a lot of
fictitious incomparabilities, hiding the true structure of the partial
order relation describing the data. It would be desirable to have
procedures to “estimate and test” partial relations. Even more
generally, I wonder which developments can be got, by systematically
introducing lattices and posets in econometrics and micro-economics,
for example taking into account that preferences can be incomparable,
not just indifferent. I think posets will have a role also in
dimensionality reduction procedures, in clustering algorithms, in
classification and in all of those tools that are gaining importance
in the field of data science.
Finally, let me mention a couple of “problems” that currently somehow
limit the use if posets. First, partially ordered sets are
combinatoric objects and working with them poses non-trivial
computational problems. So also from a computational point of view
there is a lot to be developed. Second, posets are not easy to
visualize and communicate. Hasse diagrams, the “official” finite poset
representation, become useless as soon as too many nodes and edges are
present. Is there any visual designer interested in that, out there?
Even if the language of partial orders is not so familiar to
socio-economic scientists, I see an increasing interest towards it,
also by more applied scholars. When I, and the people I work with,
have the chance to present posetic tools for data analysis and to
explain why, conceptually and technically, partial order should be of
interest, we always see much of an interest. Surely, the lack of
knowledge of discrete mathematics does not help, but social scientists
seems to be eager of new methods, for dealing with the complexity of
their problems. Also official statistical institutions are looking
with interest to the topic.
Rainer Brüggemann: Is there literature which you can recommend
newcomers?
Marco Fattore: If I were to provide some texts to go into this fascinating field, I
recommend some math books (like the classical Davey and Priestley
“Lattice and Order” and “Basic posets”; by Kim and Neggers) and some
applied volumes (like “Partial Order Concepts in Applied Sciences”, by
Fattore and Bruggemann (Eds.) or “Ranking and Prioritization for
Multi-Indicator Systems”, by Bruggemann and Patil). But more
important, I suggest to get in contact with the community of poset
researchers that is developing the topic.
Rainer Brüggemann: We thank for the interview!
Marco Fattore: You are welcome!
(Peter Koppatz and Rainer Bruggemann)
Rainer Bruggemann
