Nate Silver runs the numbers. His conclusion is ambiguous:
For Democrats, all of the t-statistics are large and positive, indicating high degrees of statistical significance. In other words, Iowa matters and provides us with salient information that is not available from the national polls. This holds even if you include (as I do) the unusual case of 1992. But for Republicans, there is no statistically significant effect from Iowa. In some of the models, the effect of Iowa is positive but not quite statistically significant. In others, it’s actually negative (although also not to a statistically significant degree)…But I think it’s sophomoric to conclude, as a narrow reading of this evidence might, that Iowa does not matter at all for Republicans.