  We use WMAP 9-year bispectrum data to constrain the free parameters of an
'effective field theory' describing fluctuations in single-field inflation. The
Lagrangian of the theory contains a finite number of operators associated with
unknown mass scales. Each operator produces a fixed bispectrum shape, which we
decompose into partial waves in order to construct a likelihood function. Based
on this likelihood we are able to constrain four linearly independent
combinations of the mass scales. As an example of our framework we specialize
our results to the case of 'Dirac-Born-Infeld' and 'ghost' inflation and obtain
the posterior probability for each model, which in Bayesian schemes is a useful
tool for model comparison. Our results suggest that DBI-like models with two or
more free parameters are disfavoured by the data by comparison with single
parameter models in the same class.
