Colin,
The first thing to evaluate are the drive time polygon drive time differences between the BA Web App and BA Desktop. BA Desktop has two broad presets in Fast and Detailed as well as other options like calculating drive times towards and away from the facility. I have been working with both products in all their variations for many years and my general expectation would be, even without testing, that the drive time polygons will be different. If someone is working with both products and co-workers with one or the other product this is a good conversation to have. Also the BA Wep App gets the latest data vintage release first so there is a time period where BA Desktop is behind (one can run online reports as well as online drive times on BA desktop) with the local data vintage till the update is released
Drive time area created by network datasets that are also updated each year so year to year comparison have to take that into question.
Another thing to consider is the data apportionment differences between the two products. In Business Analyst Desktop one has three presets (hybrid, block apportionment, cascading centroid, and not even touching the variations when creating custom BDS layers) which will all produce reports with differing values. Hybrid on BA Desktop will be very close if not exactly the same as the BA Web App (with a caveat potentially on the online side when it comes to very large areas in the past but I can be corrected on that) as long as the vintages are identical.
Regards,
Jason R.
