Thursday, November 29, 2018

Put Writing Strategy

ERN recently posted again about his put writing strategy. Despite the market falls in October he ended up for the month. This seems to be down to luck that after his contracts went into the money (which means a loss if you write options) around 12th October, they then recovered substantially before the expiry date. I was curious about the performance of such a strategy in the long term. You can now buy an ETF that implements a similar strategy. It differs a little from ERN's strategy. In particular, the ETF sells options each month, rather than 3 times a week. It tries to match the performance of the CBOE S&P 500 put writing index. The index goes back to 1986! In the following I analyze the performance of the strategy since January 2007. Looking at the chart of the index, it seems to track the fluctuations in the stock market quite closely over the last 10 years:
Most of the time there is lower volatility and then there are occasional spikes. When I regress monthly returns on the monthly returns of the S&P 500 total return index (i.e. including dividends) I get a beta of 0.64 and annualized alpha of 0.9%.* The R-squared is 0.74. After transaction costs that alpha will likely disappear. This is looking a lot like investing 64% of your money in an S&P 500 ETF and the rest in cash with occasional volatility spikes added in.

Of course, this might not be much like the return profile that ERN is getting as his performance in October shows.

 * This isn't the classic CAPM regression where you deduct the risk free rate first, but that won't make much difference here.

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