it demonstrates that time-varying expected idiosyncratic volatility has
a significant and positive effect on expected stock returns for individual stocks and stock
sectors. The study found that expected idiosyncratic volatility plays a more important
role than expected market volatility in determining expected stock returns from individual
stocks. In contrast, expected market volatility plays a more important role than expected
idiosyncratic volatility in the case of stock sectors. The advice to investors derived from
this study: First, consider the sources of market volatility before developing an
investment portfolio. Volatility might come from an economic downturn, the fluctuation
of foreign exchange rates, or political crises. Second, pick common stocks with high
idiosyncratic volatility. Third, consider risky common stocks as the first investment priority
because they have high idiosyncratic volatility that results in high expected stock returns.
This investment strategy is useful for the Stock Exchange of Thailand and Securities
Exchange and Commission in selecting companies to list on the stock market.