Probabiltiy of Car Crashes

(Originally written at Thursday, January 8, 2009 at 2:11pm)

Here is one simple thing in life that you want to note it down. It's not such a common event happened in my life. When this happened though, it will naturally keep me in deep thought.

There was a electric outage in the 3-5 blocks I lived in. My place is very close to Mass. Ave. For non-Bostonians, it's a main avenue that connect several residential regions of Cambridge Massachusetts.

The electric outage caused me to do something a bit different from my normal schedule - I went to a cafe to read and stay there until 10:10 p.m. and decided to walk back. The road is slippery. I nearly fallen down for a couple of times. But well, no big deal I just find the most snowy to put my steps on. Things are ok.

Then I heard a "bam" from my back and I took a look. 6-7 feets behind me, it turns out a van has lost control and hit on a building. Part of the wall has a 1 feet x 1 feet x 1 feet size of hole. There is a part of the building was made of steal. There is a dint. Luckily the car wasn't going too fast. So it just stops after it hits the building.

I am fair in my faculty of imagination. "What if I was hit?" and allow me to skip the description of my imagination because it doesn't look good.

I naturally wanted to leave that spot immediately. At the same time, I wanted to keep an eye on the driver and see if he was hurt. The driver gave me an "ok" gesture. Then he seems to get a grip of his wheel again. So my conclusion is the road might be too slippery and caused the whole thing.

For me, living is U.S. in general means a lot of thinking and philosophizing. Since I live with books and computers too much, I seldom come that close to a near-death experience. But I guess for many, any car accident in their lives will make them think.

Some might decide that's the moment to take up a belief. You will hear that in a lot of convictions from Bible study group or evidence of religion A, B, C. In my case though, I was thinking of the probability of how often this would happen to me.

According the car accident statistics, http://www.car-accidents.com/pages/stats.html, there are around 2.8 million people get hurt annually and 40k people died in car accidents. If we assume 330 million as U.S. population. So we are talking about an odd of 117:1 and 8250:1.

Now what are the odds of being hit and die if you are just walking on the road. (i.e. you are not a driver or passenger). Then according to statistics, there is only ~100 persons who will die like this. So the odd is around 1 million to 1 against that happens.

So 117:1 against me to get hurt makes me feel relatively happy because 117:1 is more like two consecutive drawn out by a 4 outers in Texas Holdem (~1/11). That happens often when you played 100k hands of holdem.

What about the other numbers? well, it sounds like I am naturally protected from dying anyway. In 8250:1, we are talking about someone who 4 consecutive drawn outs by a 3 outters. In the case of 1m: 1 case, that's so unlikely which lightning turns out to be more threatening to my life.

Now what about the fact that there is an electric outage and the slippery road condition, will that increase the chance of accident? Absolutely. It probably double the chance.

So what did I learn from this? Walking was statistically safer than driving. This doesn't take a PhD to figure it out. Well, but the fact that a lot of people change their life perspectives just because some unusual life events is astounding. After some semi-careful analysis, it is not such a mystery at all. These are just usual fact of life.

The event does urge me to search for a girlfriend/companion. (Umm, I don't know the probabily of *that*) Well, after all, if I live till 60, probability will dictate, there will be 1 or 2 days I will get hurt in a car accidents. Before that happens, let's make sure I have a family first. :)

Arthur

Statistically Insignificant Me

(Originally written at Wednesday, November 07, 2007)

Slightly related my last post. It relates to an interesting issue of whether we should share the bookshelf in the first place.

Why is it an issue? Well, privacy. Suppose someone is malicious and try to figure you out. The best way is to try to gather all information about you and work against you.

Another concern of mine is rather interesting and absolutely speculative, what if information I read will affect my thought and what if people could reconstruct it just from the information I read? That will open up a lot of interesting application. e.g. We might be able to predict what a person will do better.

Just like in other time series problem such as speech recognition and quantitative analysis. Human life could simply be defined by a series of time events. Some (forget the quote) believes that one human life could be stored in hard-disk and some starts to collect human life and see whether it could be model.

Information of what you read could tell a lot of who you are. Do you read Arthur C. Clarke? Do you read Jane Austen? Do you read Stephen King? Do you read Lora Roberts? From that information, one could build a machine learner to reverse map to who you are and how you make decision. We might just call this a kind of personality modeling.

It seems to me these are entirely possible from the standpoint of what we know. Yet, I still decide to share my bookshelf? Why?

Well, this was crystal-clear moment for me (and perhaps for you as well) which helps me to make a decision: Very simple, *I* am statistically in-significant.

If you happen to come to this web page, the only reason you come is because you are connected to me. How likely will that happened?

I know about 150 persons in my life. The world has about 6 billion. So that simply means the chance of me being discovered is around 1.5 x 10^-8. It is already pretty low.

Now, when other people know me and recommend me to someone else. Then this probability will be boosted up because 1) my PageRank will increase, 2) people follow my link deep enough will eventually discovered my bookshelves.

Yet, if I try to stay low-profile, (say not try to do SEO, not recommend any friends to go to my page) then it is reasonable to expect the factor mentioned is smaller than 1.

Further, 1.5 x 10^-8 is an upper bound as an estimate because
1, Not all my friends are interested in me (discounting factor : 0.6, a conservative one, the actual number is probably higher but I just don't want to face it. ;) )
2, My friends who are interested in me might not follow my links (discounting factor: 0.01)

So we are talking about an event with probability as low as 10^-9 or 10^-10 here. That seems to me close to cheap cryptographic algorithm.

But notice here, my security is not come from hiding or cryptography. My security merely come from my statistical insignificance. In English, I am very open but no one cares. And I am still a happy treebear. ;)

That's why you see my bookshelf. Long story for a simple decision. If you happen to read this, I hope you enjoy it.

-a