Another crucial mistake of the authorities was their decision to liberalize capital flows
across borders while sticking to a fixed exchange rate system and also trying to pursue an
independent monetary policy. This is, of course, the classic Mundell “impossible trinity”
(Mundell, 1963).
Thailand had successfully used a fixed exchange rate system since the end of the
Second World War. This had contributed to economic stability and was an important
foundation for economic growth for many decades. However, these successes were mostly in
a global environment of modest financial capital flows. The mistake was to stick to this old
paradigm in the 1990s when capital flows became very large and very volatile.
Before the crisis, the baht was fixed to a basket of currencies with the US dollar having
by far the largest weight in the basket resulting in a fairly stable baht/$US rate for many years
before the crisis. However, Thailand also tried to pursue an independent interest rate policy.
This can be seen from the gap between the Thai overnight interbank rate and the US overnight
fed fund rate. This gap averaged about 3.97% between January 1989 and June 1997 (the last
month before the float of the baht), and sometimes reached up to 10% (see Figure 1). With
liberalized capital flow, this inevitably led to a large amount of capital flow into Thailand.