cat /proc/claus

This year I gave lectures to three different classes about introductory statistics. One of my favorite classes was Correlation and Linear Regression, because It allowed me to talk to students about more practical applications of the usually very mystical concepts of statistics.

In all three lectures I talked about the “correlation vs causation” dillema, and in all the exams I included the following question: “A group of scientists find out that the rate of use of product X has a strong correlation with the rate of hairlessness in people. Is this result useful to say whether product X causes loss of hair? What arguments or experiments could you use to determine if X and loss of hair have a casual relationship?”

It is a very open ended question, I wanted to pick at my student’s brain and gauge how much of the class they assimilated more than I wanted an exact answer with an exact score (there were other questions for that). The results were very interesting.

As for the first part of the question, a very large number of students in all classes misunderstood the meaning of the word “useful”. They would answer that either the correlation does not prove the causation, which is correct, but is not what I was asking. Of course correlation does not prove the causation, the question itself states that! But still, it is useful information, because if the correlation was 0, we could exclude a direct causation right out of the bat.

As for the second part of the question, many, many students suggested tests with control groups to test if the causation really exists. This shows a fundamental misunderstanding of either what control groups are really about, or what about what correlation really means. If you have already stablished a strong correlation between X and hair loss, the logical conclusion is that a control group that is not using X will not show hair loss. The control group will simply confirm the correlation we already know about, and teach us nothing about the causality (or lack thereof) of X and hair loss.

This is not exactly an easy question — even though it uses no numbers or asks for no formulas! — but since I said they could use arguments instead of experiments, they could suggest different X with and without causality relationship with hair loss, and compare them. For instance, they could say that X could be either an anti hair loss product (and the causality relation would actually be inverse in this case!) or a shampoo with a bad chemical balance (and in this case there would be a causal relation) - the “experiment” in this case would be to actually investigate X and how it relates to hair loss in chemical/biological terms, and not something as simple as “Do a Z-test/double blind test/whatever”.

Things to keep in mind for the next time around…

Little Jimmy lived in a small town by a lake. One day, he went to the lake and saw a large monster coming out of the lake. The monster looked mean and hungry, and was walking toward’s Jimmy’s town.

Jimmy ran as fast as he could to his town, and shouted at the top of his lungs:
- HELP! HELP! An monster am coming from the water!

Three people (Ann, Bob and Charlie) came to see what the ruckus was about:
A> Jimmy, what did you say?
J> I said an monster am coming from the water! Help!
B> That sounds terrible!
C> Jimmy, you can’t say “an monster”, the correct way is “a monster”
B> But jimmy is young, he has the right to make such mistakes!
A> Right? Of course not, I learned how to talk properly, Jimmy should too! Also, what about the “am monster”?
B> Well, it is an accepted form in certain kinds of poetry and popular discourse, isn’t it? Little Jimmy is actually a culturally aware poet!
C> You can’t mean that, that is ridiculous!
B> You are oppressing Jimmy’s way of expressing himself!

J> Help! The monster am coming from the water!
C> What do you mean by water?
B> Maybe he means the lake?
A> But there is water in the sea too, how do you know the monster is not actually in the sea?
B> But even if the monster came from the sea, it would be a terrible happening to all of the world, wouldn’t it?
C> But the sea is so far away…
B> You are being too selfish! The people in the seaside town also deserve to be protected from monsters!
A> Well, if they want to be protected, maybe they should protect themselves… why should we protect them from sea monsters?
B> Because maybe now it is a sea monster, but next time it may be a grass monster, and come from the grass near our town!
A> I’m well protected against grass monsters. If you are worried, you should be protecting yourself.

About that time, the monster arrived and devoured Ann, Bob, Charlie, and Little Jimmy as well.

Many times, this is watch it feels like when I watch people debate politics.

Someone at team liquid forum posted a strategy guide joining two things that I love, zombies and StarCraft:

A Zombie´s Guide to Starcraft

There is some surprisingly good advice there about gaming and laddering mindset. I´ll be sure to put it to good use.

Braaaains!

We need more people in space, making more stuff like this. I find it particularly impressive the many blue flashes from thunderstorms seen in the time lapse.

Earth | Time Lapse View from Space, Fly Over | NASA, ISS from Michael König on Vimeo.

Zombies are one of my favorite things And two weeks ago I had the chance to take part in the Zombie Walk RJ 2011! (portuguese only )

For those who do not know, a zombie walk is an event where a lot of people dress like zombies, gather like zombies, and shamble the streets while moaning ¨braaaaains¨, like zombies! It is a big ¨be a zombie for a day¨ event. A light hearted and fun bloody walk!

At first, I was thinking that dressing as a zombie would be the easy part - just some fake blood, dirty clothes and we´re good to go, right? Turns out that making fake wounds can be a very complicated endeavor. I decided to try my hand at making a more elaborate costume by checking some internet turorials.

The results were mixed…

But at least I got to meet these guys!

So it was pretty fun.