It is the latest populist theory doing the rounds in the financial media. Even the mainstream media is now flooded with this now. See

here and

here

To see why it does not make much sense, we need to understand what quantitative easing actually is, in terms of Economic models.

The standard Keynesian model is the famous

IS-LM model. This captures the goods and money markets equilibrium simultaneously in an economy. The IS curve of the model, derived from the equilibrium of output and aggregate demand, captures the goods market equilibrium. It outlines the combinations of interest rates and economic output for which such equilibrium is possible. It is a downward sloping curve, as for a given level of external factors, a higher interest reduces the investment spending and hence output. The second part of the model is the LM curve. Derived from the demand of money, it captures the combination of interest rates and output for which the money market is in equilibrium. This is an upward sloping curve, as for a given amount of money stock, the demand for money goes up with higher income and lower interest. For more on this look

here for a quick introduction. The entire economy is at equilibrium at the intersection of these two curves, which implies simultaneous equilibrium in goods and money markets.

However, I think to analyze QE, it is better to switch from IS-LM model to

IS-MP. It is a variation of the IS-LM model which retains the same IS curve, but replaces the LM curve, by an MP curve (MP stands for Monetary Policy). The advantage is primarily two-folds. Firstly, unlike the implicit assumption in IS-LM model, most modern central banks do not target money stock, but rather a policy rate - which is explicit in the MP model. Secondly, the IS-LM is a bit ambiguous. Ideally the relevant interest rates for IS curve is the

real interest rate, and nominal interest rates for the LM curve. So effectively it is a bit round-about to incorporate inflation directly in IS-LM. And as we will see QE is largely about (expected) inflation. For more details on IS-MP, look

here (opens PDF and a bit wonkish)

Figure below shows a typical IS-MP curve. As mentioned before, the IS remains as it is. The MP is upward sloping. Which makes sense as most central banks uses a

Taylor Rule approach to determine the appropriate level of real rate to target, balancing output and inflation. For a central bank targeting purely a real rate (i.e. inflation targeting), the MP curve will be horizontal.

In the IS-MP model, the economic shocks can be analyzed in a manner very similar to the IS-LM model. Suppose the economy is initially at equilibrium E0 with output at potential output of y0. If there is an external negative shock to aggregate demand (like the 2008 crisis), the IS curve shifts to the left (IS' in the plot), along with a drop in output y1 (which is below the potential output) at a new equilibrium of E1. The response of the monetary authority is to shift the MP curve towards right sufficiently (expansionary policy) so that the equilibrium point E1 shifts to E2, which brings the output back to potential, but at a lower real rate (r'). How the shifting of MP to right is actually achieved depends on many things. For a normal economy with sufficiently high nominal interest rates and stable inflation expectation, manipulating the nominal rate (setting fed funds etc) can achieve it. In case of a positive shock the dynamics works in the reverse. This is what central banks do in a nutshell.

The question is what happens if the nominal rates are not high enough (the so called

liquidity trap). Or the initial shock is so large that to change real rate enough to reach the equilibrium E2, the nominal interest rate has to become negative (with a given inflation expectation). Obviously, this is not likely to work. Here the interest rate implies the general level of rates. Forcing the general level of nominal rates to negative territory is quite a challenge (if desirable at all), as people can just hold cash instead of bank deposits (thus avoiding negative interest rates, i.e. paying fees to park cash at banks).

The way out is to tweak the other component of the real rate. That is inflation expectation. If the demand is lower than potential, the inflation and inflation expectation has already started creeping towards a lower base. If the central bank can convince people that it is not going to stay low for long, and jack up the expectation, that can reduce the real rate, even at a zero nominal bound. Which in turn spark real activities. Quantitative easing is a tool to achieve just that. In fact we can express real interest rates as below (as a matter of definition):

__Long term real rates = average path over expected future nominal rates + term premium - expected inflation.__

Even at zero lower bound, the central banks can use tools to manipulate any of the three terms to achieve its objective. For example, the "

forward guidance", adopted by Fed, is a tool to manipulate the first term. General asset purchase

influence the second term. And depending on how the QE is planned and communicated it can influence the

inflation expectation. In fact the standard way how QE works is mainly two channels - a) the portfolio re-balancing channel, which compresses the term premium, and b) the inflation expectation channel. And together they can work exactly like the expansionary monetary policy in the diagram above. Even at the zero nominal bound. That is pretty much what quantitative easing is. So by definition, "Quantitative Tightening" will work in reverse.

But, we are not talking about quantitative tightening by the domestic central bank here (i.e. the Fed), but rather foreign central banks. To analyze that, we need to extend out model to an open economy.

Much of the things remain the same. The stuffs that change are two-folds. Firstly, the IS curve is now influenced by the

real exchange rate (opens PDF, a brief primer). An appreciation of dollar in real term will make imports attractive for domestic consumers and export costly for overseas consumers. So this works like a negative shock to the IS curve (domestic output), a shift to the left. Secondly, we also need to incorporate the foreign exchange market equilibrium, captured in the line BP (abbreviation for Balance of Payment). This equates the demand for foreign exchange (import over export) and supply (net FX inflows, ignoring central bank reserve changes, which is only applicable for pegged currencies or managed floats). For perfect capital mobility, this will be a horizontal line, as we can have only one interest rate at which we can have equilibrium. At every other rate, large inflows or outflows will overwhelm and restore balance. For general capital mobility, we have an upward sloping curve. The equilibrium for an open economy is achieved in the intersection of all three curves - IS, LM and BP

In such a scenario, negative demand shock can be countered as before. Assuming a floating exchange rate regime, an expansionary monetary policy, reducing fed fund target or QE as the case may be, pushes the MP curve towards the right to MP'. Given the lower rates, the new point is below the BP curve, which implies an imbalance in the FX markets. In this case, the dollar becomes cheaper in real terms, leading to simultaneous increase in net export (IS shifts right to IS') as well as improvement in current account (BP shifts right to BP'). This changes the output from y0 to y1 at a lower interest rate levels. The equilibrium changes from E0 to E2. Notice the change in real interest rate is less than the previous case. A tightening works in the reverse.

Now "Quantitative Tightening" by PBoC or other central banks, (i.e. selling of treasuries) is a totally different beast. PBoC has NOT decided overnight that it is the monetary authority for United States, and is NOT trying INDEPENDENTLY to influence the monetary policy for dollars. Nor it can change the total dollar money stocks. It is selling treasury because of its own monetary policy aim, which is to maintain the Yuan trading range.

So in effect, in the above diagram, nothing changes. No dollar monetary base, nor real exchange rate, nor inflation expectation to move any of the curves. There is a potential of changing the term premium. But assuming it is selling foreign reserves for the purpose of exchange rate targeting, it must be selling not only treasury but all other reserve currencies as well. That means it will require a huge selling by PBoC to achieve a modest increase in the term premium. Which is unlikely.

Also a QE or reverse for a large bond markets like US treasury (approx USD 16 trillion outstanding) primarily works through inflation expectation than portfolio re-balancing channel. For example, the episodes of previous QEs by the Fed actually saw a modest increase in treasury yields, but an overall reduction in real yields (as computed through breakevens). In addition, the Chinese FX reserve can be around USD 3.6 trillions on paper, but given the size of the economy and exports and imports, China must maintain a part of it as a safe guard as per

IMF recommendation (opens PDF). So effectively a much less amount is available for this so called Quantitative Tightening.

And lastly, the entire point of treasury selling of China is maintaining the FX policy. The recent capital outflows increased the devaluation pressure on China, and PBoC is selling dollars and buying Yuan to protect the range. So effectively it is keeping Yuan artificially overvalued, one can argue. And that means, if they do not do that, i.e. stops selling treasuries, that will actually have an worsening impact on the US, as USD real exchange rate appreciates and shifts the IS curve towards left.

Now enough of theories. Let's look at some hard data. How much net selling is happening anyways in treasuries - based on

TIC data as of end of June 2015.

Hardly anything that suggests "Quantitative Tightening"!

Although official ownership of long term treasuries has gone down, this is more than compensated by increase in private ownership. The only countries where we have seen total treasury ownership going down is Japan and the Switzerland + Benelux block. And on overall basis foreign ownership of treasuries is on a steady upward path, after a sizable reduction for a brief period of Taper Tantrum back in 2013.

Only Fed can do a real quantitative tightening. "Quantitative Tightening" by PBoC is mostly a nonsense.

Nevertheless, what is interesting in this entire model thingy is the dynamics. You might have noticed how the entire thing works. Any monetary policy changes in response to a negative shock in demand lowers the real rate. Similarly a positive demand shock will increase the real rate for the same potential output. Interestingly in recent times, the demand shock distribution has been highly negatively skewed (you can have a look at the real GDP distribution since 80). It is hardly a surprise ever since we have a constant downward drifts in general rates levels. Forget about

secular stagnation and other interesting theories. Even in a perfectly normal economy, a negatively skewed demand shock distribution, along with Keynesian central bank, implies rates will have a tendency to drift down and eventually hit the zero lower bound and get stuck there. There are only two ways out. Either reigniting the animal spirits and optimisms of the industrial revolutions or the post-war period. Or a higher inflation target. Else downward yields are far more likely than a sharp sell-off in rates. No matter which foreign central banks are re-adjusting their FX reserve.