The Barber Paradox

October 31, 2011

I recently listened to the Radiolab podcast on Loops that has a segment on The Barber’s Paradox:

The barber shaves only those men in town who do not shave themselves.

Who shaves the barber?

Apparently this paradox was a big issue for set theory. The following SQL works quite nicely to describe the statement “all people either shave themselves, are shaved by someone else, or don’t shave at all”:

shavedBy VARCHAR(40) REFERENCES Person(name)

INSERT INTO Person(name, shavedBy) VALUES(‘Floyd’, ‘Floyd’);
INSERT INTO Person(name, shavedBy) VALUES(‘Andy’, ‘Floyd’);
INSERT INTO Person(name, shavedBy) VALUES(‘Goober’, ‘Floyd’);
INSERT INTO Person(name, shavedBy) VALUES(‘Gomer’, ‘Gomer’);
INSERT INTO Person(name, shavedBy) VALUES(‘Opie’, NULL);

SELECT DISTINCT shavedBy AS barber FROM Person
AND shavedBy != name;

The result is:


The relational model defines Entities and Attributes on those Entities. So is the issue with the Barber’s Paradox that the language does not make a distinction between Entities and Attributes or is the self-referencing part problematic? Creating a Barber TABLE to go with the Person TABLE is the wrong approach but I think it is only wrong if a self-referencing Attribute exists. We could define a patient-doctor relationship with either a doctor Attribute or a Doctor Entity and both approaches would work fine.

The SQL solution to the Barber Paradox nicely handles additional cases like a new barber moves to Mayberry or Aunt Bee shaves some men in her spare time.


Nurturing Tiger Moms

February 2, 2011

Bryan Caplan discusses Tiger Mother Amy Chua and I’m completely on-board until he says the following:

But hasn’t all the musical practice indelibly shaped Chua’s children’s characters?  Highly unlikely.  Behavioral genetics finds roughly zero effect of parents on personality.

I think this is a misinterpretation of The Nurture Assumption. The theory states that a large part of a child’s personality is environmental, that is, “nurture” but that this influence is mostly from peers rather than parents or teachers. What I think Caplan forgets is that parents can have an impact on children by indirectly influencing who their peers will be.

For instance, parents can influence their children’s personalities indirectly by the neighbourhood they choose to live in. If I remember correctly, Judith Rich Harris claims that the age of the parent(s) and whether a child is raised by a single parent has zero impact on child personality once you correct for the neighbourhood influence.

In her WSJ article, Chua says the following:

Here are some things my daughters, Sophia and Louisa, were never allowed to do:

• attend a sleepover

• have a playdate

• be in a school play

• complain about not being in a school play

• watch TV or play computer games

• choose their own extracurricular activities

• get any grade less than an A

• not be the No. 1 student in every subject except gym and drama

• play any instrument other than the piano or violin

• not play the piano or violin.

How many of these rules do you think will significantly affect the relationship these children have with their peers? I’m guessing it is non-zero and possibly as important as neighbourhood/school choice.

Yes the title is a little “cutesy” and from the department of redundancy department but let me explain. This is a tale of two newspaper stories about graffiti. The first story is a follow-up to the Graffiti Photophrapher vs. Virgin Mobile article I previously mentioned. In the post I noted that I found it ironic that the image in question, that was supposed to represent transient street art, had the URL of an art gallery named Thisisnotashop painted above it.

I sent e-mail to Thisisnotashop with a link to the Toronto Star article. The reply I received caught me off guard. Read the rest of this entry »

Slice of the Kidney Pie

August 29, 2009

Will Wilkinson and Bryan Caplan are debating why people oppose organ markets. Caplan believes that all (or effectively all) people that understand the economics behind organ markets support it over, I’m assuming, the current heavily altruistic system. Wilkinson attempts to summarize the moral argument against organ markets as follows:

Human beings have a certain dignity that is central to the value of human life. That dignity ought to be respected, preserved, and protected. Allowing the sale of human body parts diminishes the dignity of those involved in the transaction and erodes respect for the dignity of human beings generally. Therefore, markets in body parts ought to be legally prohibited.

Read the rest of this entry »

Voting Signals and GTD

June 14, 2009

Robin Hanson over at the Overcoming Bias blog has a post about What Voting Signals. He links to a NY Times article that describes a change in Switzerland in which every “…eligible Swiss citizen began to automatically receive a ballot in the mail, which could then be completed and returned by mail.” The result of this natural experiment was that the voting rate unexpectedly declined.

Read the rest of this entry »

Sandals and Summer Tires

April 27, 2009

Today is the day. It is not the daffodils nor the bloodroot blooming, it is not the green grass nor budding trees. What truly signifies the arrival of spring is the day I wear sandals and my car wears summer tires. The winter tires were swapped for summer goodness and my sandals have come out of winter storage (i.e. the back of the closet). Oh happy day :-)

Developing Smokers Revisited

September 28, 2008

In a post about the prevalence of smokers in China I challenged the assumption that smoking is caused by misinformation promoted by Big Tobacco:

My skepticism has its roots in anecdotal evidence from a couple of scuba trips to Indonesia. A high number of the dive masters in Indonesia smoke. Misinformation does not seem to apply. These young men (all have been men) have a good grasp of health issues dealing with the risk of decompression sickness and poisonous stings (rarely lethal but painful) for themselves and the divers in their charge. They speak English and are exposed to westerners who preach the evils of smoking to them daily. Yet they smoke in droves.

A paper named So You Want To Quit Smoking: Have You Tried a Mobile Phone? provides another hint.

Using panel data from 2,100 households in 135 communities of the Philippines collected in 2003 and 2006, the analysis finds that mobile phone ownership leads to a 20 percent decline in monthly tobacco consumption. Among households in which at least one member smoked in 2003, purchasing a mobile phone leads to a 32.6 percent decrease in tobacco consumption per adult over the age of 15.

What I find most interesting about this paper is not the idea that cell phones can reduce smoking but that smoking and cell phones are somehow similar.

What I think is similar is that both cell phone use and smoking represent a type of public conspicuous consumption that takes place in a social setting. They are both social signals.