Alkahest my heroes have always died at the end

August 31, 2006

Too much water in my name, part 3: too much acid in my water

Filed under: Personal,Plumbing — cec @ 10:57 pm

Since we’re on the subject of water (again), had yet another fun experience. Earlier this week, K noticed a couple of inches of water in the pan under our hot water heater. Yep, it seems to be leaking. This is the water heater that I installed one year ago. It was a replacement for a water heater installed 4 years before by the previous owner.

The tendency of our appliances to rust, particularly the water heaters led me to test the pH. Ideally, it should be between 7.0 and 8.0 (or just neutral to slightly basic). Ours was around 5.5 or somewhat acidic. This is a reasonably common problem for people with well water and it causes all of the symptoms we’ve seen (including the degredation of all brass plumbing fittings).

Fortunately, they make a “pH neutralizer” which is really just a fancy name for a tank filled with calcium carbonate (which is just a fancy name for chalk) that water flows through. I’ve got one on order, it should be here tomorrow. Once I get it installed, I’ll see if I can get the store to honor the warranty on our current water heater and replace that too.

Too much water in my name – part deux

Filed under: Personal,Plumbing — cec @ 10:46 pm

We had a batch of thunder showers come through last night. We got about 2, maybe 3, inches here. Sometime during the evening, K and I ask each other, “what’s that noise?” Turns out we had a leak in the roof that was dripping down (and through) the second story wall, onto one of the logs making up the first story and into the breakfast room. From there it was splashing onto the door to the deck and making the noise we heard.

All of which led me to climb the 45 degree pitch of a wet/slippery roof this morning, right before heading into a meeting at the office, with a tube of roofing caulk, patching up a couple of cracked shingles. We’re getting more rain now – we’ll see how well this holds.

Dropping SAT Scores

Filed under: Social,University Life — cec @ 9:43 pm

Matt Yglesias sees the recent Washington Post article describing the fall in SAT scores after the most recent test changes and asks what’s the big deal. On the face of it, Matt makes some good points. Scores are only down 7 points (5 in reading and 2 in math) and for any given student, that really isn’t a big deal. The Washington Post article, while suggesting that there may be some underlying causes (e.g. the test changes or students not learning enough) also notes that it could be a one year blip.

I did a quick look at some of the data for the SAT. It turns out that in 2005, the mean reading score was 508 (N=1,475,623 SD=113). In 2006, it was 503 (N=1,465,744 SD=113). For math in 2005, we have a mean of 520 (N=1475623 SD=115) and in 2006, mean of 518 (SD = 115 N=1465744).

Armed with this information, and the reasonable assumption that the data are normal, we can compute the likelihood that the difference between these two years is due to random sampling of students. Let’s do a student’s t-test. For reading, we get a t-value of 37.94; for math, 14.91. The probability that the reading scores could happen by chance is 0, as in less than the epsilon of my stats package (R). For math, it’s on the order of 10^-50.

Given that, we know that there is a difference here. It’s not a statistical blip. If we look further at the data, we see that SATs are remarkably consistent as long as the test isn’t changed. Essentially, we are dealing with such a huge number of students (1.5 million per year) that blips don’t show up. So that leaves us with two possibilities:

  1. graduating seniors have gotten dumber over the past year; or
  2. the change in the test is significant

I can’t definitively disprove hypothesis 1, but given the large number of students and the general SAT consistency, I think that it is not likely to be the issue. That leaves us with hypothesis 2 – the change in the test is likely to be significant. I don’t see a way to avoid saying this is the case.

Of course, on a per student basis, the change isn’t that large, but it is real and not a statistical artifact; and it means that you can’t compare SATs for students from 2005 to students from 2006.

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