Rational at night, irrational at day?

By now it is fairly well known amongst investors that there are substantial differences in the returns of stock markets during the day and overnight when markets are closed. At night, the market return is defined by the difference between the last day’s closing price and the next day’s open. But this price difference is not driven by actual trades of investors but predominantly by the news flow overnight. So, if the news is the only or at least the main influence on prices overnight, shouldn’t markets be more rational at night and be more sentiment-driven during the day?

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