Bond Market Liquidity and Selection Bias

I’ve long been a fan of Matt Levine’s excellent Money Stuff newsletter. I’ve mentioned this newsletter here several times in the past, and on one such occasion, I got a link back.

One of my favourite sections in Levine’s newsletter is called “people are worried about bond market liquidity”. One reason I got interested in it was that I was writing a book on Liquidity (speaking of which, there’s a formal launch function in Bangalore on the 15th). More importantly, it was rather entertainingly written, and informative as well.

I appreciated the section so much that I ended up calling one of the sections of one of the chapters of my book “people are worried about bond market liquidity”. 

In any case, the Levine has outdone himself several times over in his latest instalment of worries about bond market liquidity. This one is from Friday’s newsletter. I strongly encourage you to read fully the section on people being worried about bond market liquidity.

To summarise, the basic idea is that while people are generally worried about bond market liquidity, a lot of studies about such liquidity by academics and regulators have concluded that bond market liquidity is just fine. This is based on the finding that the bid-ask spread (gap between prices at which a dealer is willing to buy or sell a security) still remains tight, and so liquidity is just fine.

But the problem is that, as Levine beautifully describes the idea, there is a strong case of selection bias. While the bid-ask spread has indeed narrowed, what this data point misses out is that many trades that could have otherwise happened are not happening, and so the data comes from a very biased sample.

Levine does a much better job of describing this than me, but there are two ways in which a banker can facilitate bond trading – by either taking possession of the bonds (in other words, being a “market maker” (PS: I have a chapter on this in my book) ), or by simply helping find a counterparty to the trade, thus acting like a broker (I have a chapter on brokers as well in my book).

A new paper by economists at the Federal Reserve Board confirms that the general finding that bond market liquidity is okay is affected by selection bias. The authors find that spreads are tighter (and sometimes negative) when bankers are playing the role of brokers than when they are playing the role of market makers.

In the very first chapter of my book (dealing with football transfer markets), I had mentioned that the bid-ask spread of a market is a good indicator of market liquidity. That the higher the bid-ask spread, the less liquid a market.

Later on in the book, I’d also mentioned that the money that an intermediary can make is again a function of how inherent the market is.

This story about bond market liquidity puts both these assertions into question. Bond markets see tight bid-ask spreads and bankers make little or no money (as the paper linked to above says, spreads are frequently negative). Based on my book, both of these should indicate that the market is quite liquid.

However, it turns out that both the bid-ask spread and fees made by intermediaries are biased estimates, since they don’t take into account the trades that were not done.

With bankers cutting down on market making activity (see Levine’s post or the paper for more details), there is many a time when a customer will not be able to trade at all since the bankers are unable to find them a counterparty (in the pre Volcker Rule days, bankers would’ve simply stepped in themselves and taken the other side of the trade). In such cases, the effective bid-ask spread is infinity, since the market has disappeared.

Technically this needs to be included while calculating the overall bid-ask spread. How this can actually be achieve is yet another question!

Market makers and executionists

There are two kinds of people in the world – market makers and executionists. Market makers are great at spotting gaps in markets, and deriving business ideas out of them. They could also be great at finding and executing solutions, but their primary skill is in identifying the gaps in the market and framing the problem.

Executionists are great at execution and problem-solving. However, they need the problem to have been defined in the first place. Their ability to spot gaps in markets and thus lay out problem statements is questionable, though.

Executionists fall under different levels. It has to do with how much ambiguity they can handle. There are some for whom the problem must be defined as well as the method to solve the problem. “here is a problem. Do a logistic regression and solve it”, you need to tell them and they will use logistic regression (assuming they are trained in the subject) to solve the problem. At the next level you have people whom you can ask to find patterns in some data, but then they will figure out that the problem can be framed as a logistic regression problem and will then proceed to solve it. Further up, you just give them a business problem, and then they will figure out what data set can be used ot solve it, figure out that doing a logistic regression will solve the problem and then they will solve it. And so forth.

Then again, the first line of this blog post is wrong. There is no real barrier between market makers and executionists. There are people who are both (good for them) and those who are good at neither. However, you realize that if you are an executionist of level i, you will need the guidance of an executionist of level i+1 or above. And that if you are a highest level executionist you will need the guidance of a market maker.