Of course the gross sales data are meaningful.  However, for the reasons we've discussed, they likely don't do a good job of estimating ownership rates.

To my mind both 27% and 30% of house sales to non-locals seem like a lot, so I don't worry too much about whether one or the other figure gets used.  These numbers will change month to month and year to year anyway, so it is often good practice to give an idea of their magnitude rather than an exact figure.

In any case, standard deviation doesn't apply in this case.  Standard deviation refers to the variation in a set of data values, preferably values whose distribution approximates a normal curve.

At any rate, I wasn't hoping to start an argument.  I was just trying to get the three of you on the same page by pointing out some of the red herrings in your path.