Selection Biases in Real World Data

So a web-page depicting the average SAT score by state has been making the rounds a little bit in Iowa. Apparently Iowans are so smart! But something seemed fishy about the data...oh, right the participation rate is 3% in Iowa, and in general states with a lower participation rate have better scores.



Now, if you take the ACT data for 2010, Iowa is around 15th, but with a much higher participation rate.



Look at Maine! Maine is ranked dead last, 51st, on the SAT list, but 5th on the ACT list, up there with a lot of East Coast states whose students didn't do so well on the SAT list. New York is 46th on one list and 4th on the other.

Why the difference in Iowa's rank? And why the huge difference in Maine's rank?

Biases in the test-takers is likely to be at work. ACT has its mothership in Iowa City, meaning that Iowa is likely to be pushing the ACT for political-economic ties. In my experience, only seasoned test-takers in Iowa take the SAT. The ACT is "good enough" for most people, but because of the additional practice and the inherent variance of the tests, you can get a higher personal best simply by more tests (personal note from an MIT grad: I took each test 6 times, once per year from 7th grade to 12th grade). Thus it is likely that Iowans hoping to get into a selective school are more likely to take the SAT. A similar effect is probably at work with the ACT in states like Massachusetts --- lower participations rates in these states are being caused by forces which select for the best test-takers and smartest students.

Making the SAT difficult to take in Iowa might help the state look the best in the SAT rankings, even though the ACT is HQ'ed in Iowa City. But most of all, reading too much into improperly gathered rankings is dangerous.

The Design of Everyday Diabetic Things

I figured I'd talk a little bit of the design of things used to treat insulin-dependent diabetes mellitus (IDDM). The equipment features interesting trade-offs between ease-of-use, safety, cost, effectiveness and comfort. There are two main sets of tools: one for checking glucose and one for injecting insulin.

The Glucose Meter

There are many different glucose meters, but I use a Bayer Contour, because that's what the doctors suggested. The meter requires a disposable strip every time I want to check my blood sugar. I insert the strip into the meter, and then hold a drop of blood to the test strip intake.


The gadget is the meter, the plastic container (above the gadget) holds the test strips, the lancer is used to prick fingers (I guess they didn't want to call it a finger pricker for whatever reaon), the mesh compartment holds microlets (finger prickers), and I have some alcohol swabs in the little compartment.


The meter with a test strip inserted. In order to get a reading I have to hold a drop of blood to the little chamber at the bottom of the strip.

What the meter looks like after a reading. I'm using mmol/L, not mg/dl, which is why the reading is so low. A person with blood glucose levels of 5 mg/dl would be in a coma.


The lancing device (finger pricker) with the cap off, along with an uncapped microlet and a capped microlet. You have to twist the cap off the microlet in order to use it; if a child swallows a capped microlet, the plastic is strong enough that the cap shouldn't come off. I think. I'm not really sure, and I'm not planning on running tests, but if you know a child who would be interested in swallowing one, please feel free to contact me.

The amount the microlet penetrates into your skin is adjustable via screwing the cap on the lancing device. Diabetics who prick their fingers a lot develop callouses, so depending on the thickness of the skin, the needle may need to penetrate farther.


I had initially thought the meter was really nice. They're really inexpensive, have some fancy features like alerts, and it is very easy to use. However, much like printers being cheap and ink being expensive, the meter is cheap but the microlets and test strips are very expensive. The microlets and strips cost about a dollar a piece, and IDDM people are supposed to check their blood sugar at least four times a day. You're also supposed to change the microlet (the needle used to prick your finger), as the microlet gets worn after use. In practice most type 1s I know only change the microlet once per day. Anyways, the $20 meter consumes over $1,000 of test strips per year (my insurance covers the use of about 1,600 test strips per year). Right now I'm checking my blood glucose levels about 7 or 8 times a day, since I'm still getting used to everything, but eventually it should go down to four or five times a day. If my insurance didn't cover the strips, I'd almost certainly use a meter with a strip disk, since they'd be cheaper long term.

Overall I'm pretty happy with the meter. It is a little bulky, so I'll probably pick up a smaller one that I could carry with me, but the fact that it was free and the strips are mostly covered by my insurance makes me happy.

Insulin pens

Once per morning and before every meal I have to give myself insulin. There are two types of insulin I use. Lantus, which acts very slowly over the course of about 20 to 24 hours, is called a basal insulin. I use Lantus once per day in the morning, though eventually I'll probably have to split it into a day and night dose. Apidra, which acts very quickly, is called a bolus insulin. I take Apidra before meals; the exact dose depends on the carbs in my meal, my current blood sugar, and the amount of sugar I expect to burn. The location of injection has an important role in how fast my body absorbs the insulin. Injecting in the thighs makes absorption quite slow, while the belly area absorbs quickly. I normally use my thighs for the slow-acting, and my belly for the fast acting. I have to rotate the exact site location, or else scar tissue builds up which can make absorption difficult.

The biggest danger with the pens is that I accidentally confuse the two types of insulin. While the pens are visually distinct, with different colors, I actually wish they were physically distinct --- in other words, the Lantus pen was larger than the Apidra pen. I'm not too worried about confusing the two, since I keep them in different spots, but it would be nice if they were more difficult to confuse.


I have my two pens with two sealed needles on the kitchen table. The pens are disposable; after the pen runs out of insulin, I throw them away. Before use, the pens have to be stored in a fridge. After use, the pens are good for 28 days. I write the date the pens expire after the first use, so I can easily track when I'm supposed to throw them away. The pens are small enough to fit in my pocket.


This is the dial on one of my pens. I choose the number of units to inject by rotating the dial.

This is where the needle screws onto the pen top, with the number of units of insulin units left in the pen displayed.

This is the needle after the seal is taken off. There are screw threads on the inside that screw onto the top of the pen. The needle is inside the plastic container, so it is quite difficult to prick your finger with this. If the needle falls, it won't jab anything.


The needle has two caps, an outer and an inner. The inner cap is color-coded to the size of the needle. Different injection sites require different needle sizes.

A 8mm and a 4mm needle attached to the pens. Before injection, two units are supposed to be "burned," or injected into garbage. Burning the units insures that no air is in the needle. My Apidra pen always has a small amount of pressure, which is why there is a drop of insulin on the end.

I think the pens have a phenomenal design. First of all, the screw cap allows the use of different needles. This is important because, as I previously mentioned, different sites require different needle sizes, and because the needle wears after use, a new needle is required every time. The screw cap doubles as a safety measure; you have to push and screw the needle at the same time to get the cap on, which kid-proofs the pen to a large extent. With a child, the real danger isn't that a kid plays with the needle; the real danger would be a kid injecting themselves with insulin. The screw dial also kid-proofs the pen to a certain extent. An additional feature is that as you inject, the screw dial resets to zero. This means that the default state of the pen is going to be to inject no insulin.

The injections are almost pain free. Insulin injections are subcutaneous, compared to vaccinations which can require injecting into a muscle. I barely notice them afterwards, which has contributed to how quickly I've gotten used to them. The needles and pens, while expensive, are also (almost completely) covered by my insurance.

As I stated earlier, the devices feature some interesting trade-offs. Overall, I've been very impressed by how little pain I've experienced. While I still wouldn't wish IDDM on anyone, it isn't as difficult to deal with as I had initially envisioned. However, my pancreas is still working at some fraction of capacity, so I'll have to wait and see if I think the devices are effective enough when my pancreas produces no insulin.

Diabetes FAQ

I'm getting a lot of questions about type 1 diabetes; I figured a blog post would be in order.

What is diabetes? What is the difference between the types?
The two types of diabetes mellitus are actually quite different, though both diseases relate to sugar and sugar metabolism. Type 1 diabetes mellitus, which I have, occurs when the immune system attacks the portion of the pancreas that produces insulin. Insulin is necessary for the body to metabolize sugar correctly. Type 2 diabetes mellitus occurs when the body doesn't respond correctly to insulin. Type 2 usually occurs in older, overweight individuals that have eaten a lot of sugar.


What's up with the mellitus at the end of diabetes mellitus?
There is another form of diabetes called diabetes insipidus, or DI. Mellitus means sweet, whereas insipidus means tasteless. The terms relate to the fact that urine from a person with diabetes mellitus, or DM, is sweet (due to the sugar flushed out of the body), whereas urine from a person with diabetes insipidus is tasteless, or tastes like whatever urine tastes like. My high school biology teacher once told me that to diagnosis whether problems were DM or DI, people drank the urine. Is it true? I have no idea.

The symptoms of DM and DI are similar, but the causes and treatments are very different. Diabetes, in general, usually refers to diabetes mellitus.

What does having type 1 diabetes entail?
Essentially I have to give myself insulin instead of relying on my pancreas to produce it for me. This means that before eating anything with carbohydrates I have to give myself insulin. Anything with sugar or starch is high in carbohydrates, so foods like potatoes, candy, and fruity drinks require giving myself more insulin than meat or low-sugar foods.

Do type 1s ever develop type 2 symptoms?
"Very rarely." is the response I've received from doctors.

Isn't type 1 called juvenile-onset diabetes?
Onset of type 1 can occur later than age 40, and thus the terms juvenile or juvenile-onset are no longer preferred. Type 1 is often called insulin-dependent diabetes mellitus or IDDM. I was 26 at onset, and I know another type 1 who was diagnosed when he was 29. Type 1 is actually "better" when it occurs later in life; when kids are growing it is difficult to find the correct amount of insulin to use.

You have to give yourself a shot before you eat almost anything? Does it hurt? How much insulin do you use?
I do have to give myself a shot before every meal. I also give myself a shot in the morning of long-acting insulin that stays in my system for about 24 hours. The shots hardly hurt at all, and I have very quickly gotten used to them. I have also gotten used to pricking my finger to check my blood sugar. Pricking my fingers was worse at first, but is no longer a problem.

Right now my pancreas is still producing some fraction of the insulin that would be expected. However, my body will continue to attack portions of my pancreas, and eventually it will produce only trace insulin. I'll have to inject more insulin at this point.

The amount of insulin I use depends on the amount of sugar in the food I eat. I have to match my insulin dose to the amount of sugar in the food I consume using a carbohydrate-to-insulin ratio. The ratio will change as my pancreas shuts down, but it should stay the same afterwards.

What are the symptoms of being type 1 diabetic?
The insulin shots are to keep my blood sugar at roughly the level of a normal person's blood sugar. There are no symptoms if my blood sugar stays in the normal range. Problems arise if my blood sugar is too high or too low.

If my blood sugar goes too low, I notice it immediately, and I have something that has a little bit of sugar in it. I'm trying to find something with sugar that I don't like --- giving myself a reward when I don't properly manage my blood sugar seems like a bad idea. When my blood sugar is too low, my head feels a bit weird and my muscles jerk instead of operating smoothly. If my blood sugar goes way too low, very bad things can happen, such as fainting. Having low blood sugar is dangerous short term.

If my blood sugar goes too high, then I usually have trouble focusing. If it stays too high, then I usually itch. The itching is a personal symptom, which many people do not have. If it stays too high for too long, I can develop more symptoms, from the mundane like increased acne and increased thirst to the severe symptoms of weight loss, muscle aches and very blurry vision. My body has acclimated to high blood sugar, so it is difficult for me right now to notice when my blood sugar is high.

If my blood sugar is too high long-term, there are many complications for my eyes, kidneys, heart and lungs.

How did you find out?
Over the past three months at work, I've had tremendous difficulty focusing. I've also noticed that I've had increased amounts of acne.

During winter vacation, I spent a week in Boston. My hands started to itch, and while I didn't think too much of it at the time I did see a doctor when I was home in Iowa a week later. I starting having the more severe symptoms, including increased thirst and blurry vision. I thought my vision was blurrier than normal, but I've also needed glasses for a while, so I didn't really notice it. Then my muscles starting being sore when I walked up the stairs. I searched for the symptoms using my search engine of choice and there it was: diabetes. I saw the doctor the next day. My blood pressure was normal, my heart rate was normal, and my blood sugar was 4x the value it was supposed to be. Based on my age, weight and blood sugar, it was an automatic type 1 diabetes diagnosis. I had also dropped 2.5 kilos (about 5 pounds) in the week between the two doctor appointments. The doctors said that the decreased exercise (I ride my bike / walk a lot in NL) combined with my root beer, birthday cake and chocolate diet caused a huge spike in my blood sugar.

How does exercise work?
Blood glucose levels drop automatically during exercise, so I am supposed to only give myself a half dose of insulin at meals before I work out. After I get my levels stabilized I think I am going to join a gym.

Can you still drink alcohol?
Yes, but alcohol is tricky. Most alcoholic drinks are just fermented sugar, and consuming small amounts of sugar over a long period of time does not match giving a single injection of insulin, which works well for a meal. Additionally, being intoxicated is much more dangerous now than before. I didn't consume alcohol in large quantities before, just a beer every now and then, but I think I am going to consume even less now.

This all kinda sucks.
That is not a question, but yes, it is unfortunate. However, it turns out that people can adapt very quickly to adverse circumstances. I can tell that I am going to be able to live a normal life sans some special things required for eating food and exercise.

How common is type 1 diabetes?
In northern European populations, the rate is almost 1%, or 1 in 100 people (see the study in the next question). In America the rate is probably closer to 1 in 200 or 250 people (see the Wikipedia article). I haven't found great information on the rest of the world.

Is the disease genetic?
There are some very interesting studies on this question, particularly a study on Finnish twins. When a twin of an identical pair had type 1 diabetes, there was roughly a 50% chance that the other twin would also have the disease. There are multiple genes involved, which make occurrence complicated to predict. The 23andMe page on type 1 diabetes is actually a really good resource on the genes and appropriate studies.

Type 2 is also somewhat genetic, but is much more influenced by the environment, especially diet and exercise.

If your pancreas isn't working does that mean you don't need it? Can I stab it?
Only a portion of my pancreas isn't working; I still need some of the other portions. No, you may not stab my pancreas.

Do you expect that anyone is going to develop a cure in your lifetime?
No. It wouldn't surprise me if someone came up with a vaccine, but I doubt there will be a cure. Drug companies aren't very interesting in curing things, they care more about treating symptoms, which is a better income stream.

What was treatment like before insulin?
Controlled starvation was the "treatment" before insulin. I use quotes because nothing was actually treated, symptoms existed, but people would live longer. The life expectancy after diagnosis without starvation was about six months; it could increase to a few years with controlled starvation.

After insulin was successfully extracted in 1921 (the extraction technique's inventors won the Nobel prize in 1923), treatment was an insulin injection before any meal. I would recommend reading the book Breakthrough, though make sure you read the book's afterword to understand that some of the non-scientific portions of the book are fictionalized.

What can I do?
The most important thing you can do is take care of yourself so that you are less likely to develop type 2 diabetes. Eating foods with less added sugar, eating lots of fruits/veggies, having a balanced diet, and getting enough exercise are very important.

If you like you can donate money to a foundation like the JDRF or ADA, but I think being supportive of scientific research and politicians who support research is more important.

Finally, just treat anyone who is diabetic just like a normal person with specific dietary restrictions. Try not to confuse type 1 with type 2; while both types share the label of diabetes mellitus, the two types can be very different. If a diabetic suggests eating at a different time or a different place please accept.

Oh, and be very careful about brunch. We the type 1 diabetics hate brunch. Well, mostly hate brunch. It is too much food of the wrong type at the wrong time.

This is all really interesting, where can I find more information?
I would suggest browsing the JDRF website first, then maybe the ADA website. There is always the Wikipedia.

Worst Birthday Present Ever

I found out I have Type 1 Diabetes Mellitus just after my 26th birthday. I am fine, please don't worry, it is just going to be a huge lifestyle adjustment in the coming months.