Tuesday, July 22, 2014

We need more stats, stat

Tabarrok: Diversified stock portfolios have earned 7% on average, but with a large standard deviation. Even if you follow a buy and hold strategy, almost 70% of the time (more than 2/3) you will get less than 7%. In fact over 30 years, nearly 10% of all portfolios will lose money. The average portfolio return includes a handful of enormously large winners, so that the median return is only 5.1%. As one comment on the post pointed out: "Have you ever heard someone says that when you are young you should invest in stocks because even though they are risky you will have time to cancel out the ups and downs? Sure, you have, even someone as smart as Burton Malkiel has made this argument. Alex’s post shows that this common argument is wrong."

Blattman - Science magazine is now requiring empirical work to pass a statistics editor fluent in your empirical methodology. He notes, and I agree wholeheartedly: "In particular, I think that a 21st century undergraduate degree in social science ought to require fluency in statistics. It’s such a fundamental part of science, medicine, social science, and even reading the newspaper."

Henderson comments on McArdle's post about the choice between a 15-year and 30-year mortgage: 
"If you expect higher inflation in the future and you expect that inflation to stay at that higher level, that argues for the 30-year mortgage over the 15-year mortgage because the 30-year mortgage leaves more principal for inflation to whittle away. Other than a handful of gold coins, I have few good inflation hedges. My fixed-interest-rate loan is one of them. The more slowly I pay it off, the longer I keep my inflation hedge."
Goldstien - Benford's Law tells us that the first digit in a lot of numbers is more likely to be a 1 than a 9. Goldstien tells us how to use that information to double-check the survey information we have gathered. A comment usefully adds: "There is also a Stata package called firstdigit that will run Benford's Law tests for you: http://ideas.repec.org/c/boc/bocode/s456842.html."

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