Sunday, May 13, 2012

Network analysis of Bordeaux wine critics

Last week I provided a brief network analysis of the characteristics of single-malt Scotch whiskies. Today I wish to consider fermented rather than distilled products, and to move on to an analysis of the commentators rather than the actual products. I will do this by looking at the red wines from the Médoc region (the so-called "Left Bank" of Bordeaux, France) from the 2004 vintage. There are people who think that these are the best wines in the world, but as an Australian I find this attitude naïve.

The data to be analyzed are taken from the bordOverview (Bolomey Wijnimport) website: They consist of quality ratings of 27 wines by 7 expert commentator groups (associated with wine magazines or newsletters), these scores being awarded in September 2007 (when the wines were evaluated for "en primeur" sale):
United States of America
  Wine Advocate (Robert Parker)
  Wine Spectator (James Suckling)
United Kingdom
  Jancis Robinson
  Decanter (Steven Spurrier, James Lawther, Serena Sutcliffe)
  Tast (Michel Bettane, Thierry Desseauve)
  La Revue du Vin de France (Bernard Burtschy)
  Le Point (Jacques Dupont)

The scores have been converted to a 0-100 scale (many wine commentators use idiosyncratic scoring schemes), and all wines were evaluated by all commentators. (Many more wines were evaluated, but only 27 were evaluated by all of the commentators.) The manhattan distance measure was calculated between each pair of commentators, and the result displayed as a NeighborNet network. People who are closely connected in the network are similar to each other based on their scoring patterns, and those who are further apart are progressively more different from each other.

Click to enlarge.

Note, first, that there is considerable conflict among the critics — they certainly don't agree with each other uniformly. Wine tasting is an art not a science.

Second, note that the biggest split (bipartition) separates the English- and French-speaking commentators from each other, with the exception of Jancis Robinson, who is apparently a Francophile. The French clearly do not have the same view of their wine as do some other people.

Finally, there are some long terminal edges, indicating that a lot of each opinion is unique to that commentator, except for James Suckling, who apparently has fewer opinions of his own. As I noted, wine tasting is an art not a science.

This analysis was an exploratory one, looking for shared data patterns. It seems worthwhile, however, to pursue the origins of these differing expert opinions. That is, we need a directed graph rather than an undirected one. If we nominate Robert Parker as the outgroup to the others, as he obviously is to anyone who knows about him, then we can produce a rooted reticulation network using the method of Huson et al. (2005, Lecture Notes in Bioinformatics 3500: 233–249). In this diagram the blue lines indicate "hybridization" histories.

Click to enlarge.

There appear to be three hybrid results, so that there are four "pure" wine evaluations and three "hybrid" ones. First, the Decanter opinion (Spurrier_Lawther_Sutcliffe) is a combination of the opinions of the Wine Advocate (Parker) and Le Point (Dupont) + Robinson. Second, the Wine Spectator scores (Suckling) are a hybrid of those of the Wine Advocate and Tast (Bettane_Desseauve). Third, the Revue du Vin de France outcome (Burtschy) is a hybrid of Robinson's and Tast's. Note that each of these hybrid opinions is a cross-cultural (French-English) mixture! The world of wine truly is international.

I think that this adequately sums up the world of wine criticism. Everyone's opinion is mostly someone else's, modified in response to someone else again.

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