Thanks for both the general praise and the specific critiques.

On Salganik’s MP3 experiment, I’m also a very big fan of this project. I cite/discuss it several times but it’s mostly in the endnotes so it’s easy to miss. Probably the most extended discussion is note 42 to ch 3. However you’re totally right that in none of these cases am I laying it out on its own terms, more that I’m using it to support or contextualize a specific point in my own argument. This was driven by the choice to structure the book as a positive work rather than a review piece, though of course it’s entirely possible that I could/should have worked a more extensive review into the intro. I do consider the Salganik papers to be incredibly important findings though and the third lecture of my undergrad course is about why quality is only loosely coupled to popularity, just as I have also blogged similar thoughts.

As for the “essentially fixed population size during the time span of a diffusion episode” assumption, for better or worse I like to hold discussion of assumptions towards the end. Again, a debatable approach. I’m actually not sure though how much it matters. If you look at pp 36-39 of the Mahajan + Peterson green book on diffusion, you see that adjusting the Bass model to accommodate a growing population is fairly trivial. For other diffusion models (especially those that are operationalized at the micro-level as network contagion) this could be a serious scope condition, but as I argue in ch 4 I’m somewhat skeptical of those models anyway.