nineteenth century (Markham, 1997). Consumers can thus be assumed well informed about the
quality of the wine that was produced in the past. Quality of the wine is however likely to vary
from one vintage to another due in particular to the weather conditions that prevailed during
the grapes-growing season.2 There is thus some uncertainty remaining about wine quality when
the "primeur" market opens, and consumers are thus likely to rely on experts’ opinion. If the
producer believes that the consumer’s willingness to pay for the product is influenced by experts’
judgment, then he might price the good accordingly.
The main issue of this empirical work is that true quality, which is known by the producer
but unobserved by the consumer and the econometrician, will not only influence the pricing of
"primeur" wine, but true quality is also likely to be correlated with experts’ reviews. We thus face
a typical problem of omitted variable which may produce biased estimates if not controlled for.
This endogeneity problem cannot be solved through natural instrumental variables techniques
because it would require the availability of variables correlated with experts’ grades but not with
wine quality. Reinstein and Snyder (2005) faced the same endogeneity problem when measuring
the influence of movie critics on consumer demand, since, as stated in their paper, “products
receiving positive reviews tend to be of high quality, and it is difficult to determine whether
the review or the quality is responsible for high demand”. To circumvent the problem these
authors take advantage of the timing of the reviews relative to a movie’s release. Indeed, some
reviews came during the opening week-end while other reviews came only after. A differencein-
differences estimator was thus applied using observations fromthis quasi-natural experiment.
The validity of this approach relies on the assumption that the selection of movies to be reviewed
during and after opening week-end is not correlated with quality reviews. The authors provide