Big Brains needed for math/graphing problem

I need to try to infer the best-guesstimate overall rate of appreciation per month of industrial properties in our city from mid-2006 to mid-2007. The problem is, I have only one sale which sold in 2006 and was sold again in 2007. It implies a 2.25% per month increase. Gut tells me this is about right, but I need to try to prove it.

I have a set of data. The data represents industrial properties that have sold, and then resold over the past several years.

It’s my hope that the big brains at the Dope could help me figure out how either to calculate or to graph in such a way that supports (or discredits…but hopefully supports) that the industrial market appreciated at 2.25% per month from '06 to '07. Below is the categories of sales I have, the number of sales, and the median of the properties’ monthly increase (simple, not compound).

Bought 2002 Sold 2004 – 4 sales – 1.04% / mo.
Bought 2002 Sold 2005 – 4 sales – 0.88% / mo.
Bought 2002 Sold 2006 – 4 sales – 1.53% / mo.
Bought 2002 Sold 2007 – 5 sales – 1.57% / mo.

Bought 2003 Sold 2005 – 5 sales – 2.05% / mo.
Bought 2003 Sold 2006 – 1 sale – 3.48% / mo.
Bought 2003 Sold 2007 – 3 sales – 2.08% / mo.

Bought 2004 Sold 2005 – 3 sales – 1.59% / mo.

Bought 2005 Sold 2006 – 3 sales – 2.87% / mo.

Bought 2006 Sold 2007 – 1 Sale – 2.25% / mo.

My solution doesn’t need to be mathematically incontrovertible, only a reasonable interpretation given the limited real-world data available. My gut tells me that the market was warming up in 2002-2004, the greatest increases occurred in 2005-2006, and the market had cooled down for 2006-2007.

Please Big Brains, use your powers for good and assist this poor soul. Because this thing makes me want to stab my eyes with knitting needles just so I don’t have to look at it anymore.

If you want to gauge the appreciation for 06/07, the first thing you need to do is throw away the sales that are too early. You should have exactly one sale before 2006 for each property (except the last one, where you have no data). Check your data after you do that and see how reasonable your hypothesis looks. What you really want is a statistician in here.

You can’t draw any conclusions from one sale in a time period.

It’s the norm in assessment to look at all resales as one of the indicators of appreciation. Unfortunately, we do only have the one in 2006-2007.

Unfortunately, I HAVE to. I won’t be relying solely on a resale analysis to derive my time adjustment, but have to come up with some kind of a conclusion from these sales. I know that it will be weak, given that there is only the one sale. But I will need to give an argument regardless.