Laube versus Suckling — do their scores relate to wine price?

The short answer is: yes, and no!

A few weeks ago I wrote about the wine-quality scores from different professionals, and what their differences might mean for us (Laube versus Suckling — their scores differ, but what does that mean for us?). Another issue of importance to us is whether wine quality scores are related to the prices of the wines — after all, wine could never be good value for money unless higher prices reflect higher quality. So, an obvious follow-up question is whether critics' scores relate to the prices of the wines being tasted.

I have written before about the relationship between wine price and quality (The relationship of wine quality to price), noting that this often follows a simple exponential relationship, as QPR (quality-price ratio) so often does in economics. I have also noted that wine prices often have at least two very distinct price categories (Luxury wines and the relationship of quality to price), with different quality-price relationships. Both of these concepts are relevant to this blog post.

The data I am looking at here is the same as for the prior post concerning James Laube and James Suckling, when they both worked for the Wine Spectator magazine. These data are from the "Cabernet Challenge" of 1996 (see Wine Spectator for September 15, 1996, pp. 32–48), in which the two James tasted 10 California Cabernet blends and 10 Bordeaux red wines from both the 1985 and 1990 vintages. This gives us 40 bottles of wine with which to compare their scores, along with the prices of those same wines, as given in the magazine article.

These data are shown in the first graph, with each point representing a single wine, with its price indicated vertically and the quality score indicated horizontally. Note that each wine appears twice in the graph, once for Laube's score and once for Suckling's (they will thus appear as horizontal pairs, since the pairs have the same price).

The main thing to notice about the data at this stage is that there there are clearly two wines whose prices are disconnected from those of the other wines — Château Margaux 1990 (the pair of points at the upper left) and Château Latour 1990 (the pair at the upper right). Of these two wines, the Château Margaux is a rip-off according to both critics, as its price is completely out of line with their assessment of its quality. Indeed, this wine was singled out in the magazine article as being especially "disappointing".

We can now look at the price-quality relationship of the remaining wines (ie. ignoring these two "luxury" wines), as shown in the next graph.

At first glance, there does not seem to be any clear relationship between quality and price — wines with lower quality (at the left) seem to cover a wide price range, as do wines with higher quality (at the right). However, there are actually two factors obscuring the expected relationship here (higher quality for higher price).

The first factor is that James Suckling's scores do show a relationship between quality and price while James Laube's do not. This is why there is a "yes and no" answer to the title question — "yes" for Suckling and "no" for Laube. Formally, the mathematical correlation between wine price and quality for Suckling is 18% while it is only 1% for Laube. [Note: 18% is still not a high value; see below.]

The reason for this difference in the two James is shown in the next graph, where I have drawn ovals around three of Laube's points. These three points are what we call "influential values", in the sense that they strongly affect his QPR correlation — without these three values his correlation would also be 18% (as it is for Suckling).

The two points at the upper left are two Bordeaux wines that Laube scored very low compared to Suckling (Château Mouton-Rothschild 1985, Château Margaux 1985) and the bottom right point is a California wine that Laube scored much higher than did Suckling (Beringer Private Reserve 1990). In all three cases, Laube's score is out of line with the wine price whereas Suckling's score matches the price more closely.

The second reason for a wide spread of points is indicated by the box I have drawn around the pair of points (in the graph) for one of the wines. This wine (Chateau Montelena Napa Valley 1990) is the most obvious bargain among the wines — it has a high score from both critics but is one of the cheapest of the wines. This is a case of quality being high but not price.

Finally, the line drawn on the graph represents the exponential relationship between price and quality for the remaining wines (ie. ignoring Laube's influential values). That is, price does generally increase with quality, with a correlation of 24% (as indicated on the graph). In other words, about one-quarter of the variation in wine price is correlated with wine quality (irrespective of which of the two critics provides the score).

I will leave it to you to think about what the other three-quarters of price variation might be related to!

Conclusion

There are four conclusions from this dataset, which may be true for other data, as well. First, there are luxury wines whose exorbitant price is unrelated to their quality. Second, some critics have scores that are related to price, while others do not. Third, wine bargains can be found. Fourth, only about one-quarter of wine price is related to quality.

I doubt that more recent wine scoring is any different from this (although the prices now are certainly higher!).