## August 10, 2006

### Birthday Serendipity

I had two serendipitous moments today, both relating to my thesis.

First, I'd been feeling stuck for the past couple of days. I am working on a way to translate this new model approach I've designed into a computational model. This is the last part of the last revision of my thesis, and the phrase "always darkest before the dawn" comes to mind. I've got the logical steps of the model down and now I need to figure out how to represent that in the analytical program I'm using. It's not really a huge deal, since I'm using a very simple add-in to Excel -- not like I'm writing my own code or anything -- but it's proving to have its own challenges.

I'm working on trying to attribute human cases of Salmonella illness among the various food commodities to identify where most of the Salmonella is coming from. Now, there is a lot we don't know about where Salmonella is and how it works its way through the food production systems. It's a bit like a black hole, really. What I'm trying to do is identify ways we can nibble away at the edges of this black hole now, with the data we have, and how we could get even further with more information and better data.

Cutting to the chase, I had come to a point yesterday when I realized I needed to account for all the different combinations of foods the cases had been exposed to just prior to getting ill. I was pretty sure I new how to puzzle this out using simple probability rules, but I went to my book to make sure.

I learned that what I wanted to know was the number of subsets that exist for the nine food categories in my model. It turns out there is a shortcut to calculating this: it is simply 2^n (2 to the nth power). So I learned I would be working with 2^9 = 512 possible combinations. As I continued reading, I also rediscovered how all of these combination ideas fit into Pascal's triangle. I say "rediscovered" because I had learned about Pascal's triangle in math class, but I don't think I really appreciated its beauty until now.

But I haven't even come to the real serendipity yet. There were also a couple of lines in the combinations section that I skimmed over and then re-read, concentrating on their meaning: "A subset may be chosen by deciding for each of the n elements whether that element should belong to the subset, or not. There are n successive choices to be made, with two possible choices at each stage." Those two sentences have given me an idea for a whole new way of setting up this analytical structure -- one that may save me the step of having to create all 512 possible combinations.

The funny thing is that when Ben and I were carpooling into work this morning, and I was complaining about being at a complete mental logjam, Ben said that I would come up with a great idea today to get me unstuck.

Maybe it's all due to birthday karma. Which brings me to serendipitous moment number two.

I don't make a habit of reading my horoscope. But today I decided to see what my birthday horoscope said. Here it is from The Washington Post. (I didn't know the Washington Post had horoscopes, but they do, filed under "Arts & Living".)

### Leo July 23 - August 22

For Thursday, August 10 -You have been moving forward on a new goal for quite a while, and should start seeing real progress today. If you don't feel like you are far enough along then backing out of this situation is not an option. You are in the thick of things, and you might as well keep on going -- things will start looking more promising soon. Right now you can try to get more comfortable with your surroundings if you understand the processes going on. Ask a few questions and get informed.