In this question's title, I reported the daily highs for CHK for June 5th 2020 ($25.95), 8th, and 9th. CHK had been rumoured to file for Ch 11 bankruptcy since March 2020(?), and it did on June 28. This article and r/stocks purports to explain these swings, but how would the EMH explain, or fail to explain, these swings?

I quote A Random Walk Down Wall Street: The Time-Tested Strategy for Successful Investing (2019 12 ed), ch 7. If you know the page number, please edit this post!


The academic community has rendered its judgment. Fundamental analysis is no better than technical analysis in enabling investors to capture above-average returns. Nevertheless, given its propensity for splitting hairs, the academic community soon fell to quarreling over the precise definition of fundamental information. Some said it was what is known now; others said it extended to the hereafter. It was at this point that what began as the strong form of the efficient-market hypothesis split into two. The “semi-strong” form says that no public information will help the analyst select undervalued securities. The argument here is that the structure of market prices already takes into account any public information that may be contained in balance sheets, income statements, dividends, and so forth; professional analyses of these data will be useless. The “strong” form says that absolutely nothing that is known or even knowable about a company will benefit the fundamental analyst. According to the strong form of the theory, not even “inside” information can help the investors.
      The strong form of the EMH is obviously an overstatement. It does not admit the possibility of gaining from inside information. Nathan Rothschild made millions in the market when his carrier pigeons brought him the first news of Wellington’s victory at Waterloo before other traders were aware of the victory. But today, the information superhighway carries news far more swiftly than carrier pigeons. And Regulation FD (Fair Disclosure) requires companies to make prompt public announcements of any material news items that may affect the price of their stock. Moreover, insiders who do profit from trading on the basis of nonpublic information are breaking the law. The Nobel laureate Paul Samuelson summed up the situation as follows:

If intelligent people are constantly shopping around for good value, selling those stocks they think will turn out to be overvalued and buying those they expect are now undervalued, the result of this action by intelligent investors will be to have existing stock prices already have discounted in them an allowance for their future prospects. Hence, to the passive investor, who does not himself search for under- and overvalued situations, there will be presented a pattern of stock prices that makes one stock about as good or bad a buy as another. To that passive investor, chance alone would be as good a method of selection as anything else.

      This is a statement of the EMH—the efficient-market hypothesis. The “narrow” (weak) form of the EMH says that technical analysis—looking at past stock prices—cannot help investors. Prices move from period to period very much like a random walk. The “broad” (semi-strong and strong) forms state that fundamental analysis is not helpful either. All that is known concerning the expected growth of the company’s earnings and dividends, all of the possible favorable and unfavorable developments affecting the company that might be studied by the fundamental analyst, is already reflected in the price of the company’s stock. Thus, purchasing a fund holding all the stocks in a broad-based index will produce a portfolio that can be expected to do as well as any managed by professional security analysts.
      The efficient-market hypothesis does not imply, as some critics have proclaimed, that stock prices are always correct. In fact, stock prices are always wrong. What EMH implies is that no one knows for sure if stock prices are too high or too low. Nor does EMH state that stock prices move aimlessly and erratically and are insensitive to changes in fundamental information. On the contrary, the reason prices move randomly is just the opposite. The market is so efficient—prices move so quickly when information arises—that no one can buy or sell fast enough to benefit. And real news develops randomly, that is, unpredictably. It cannot be predicted by studying either past technical or fundamental information.

  • $\begingroup$ Hi! Why do you feel the EMH should explain these price movements? Even immediate and perfect information about company would not imply constant prices. $\endgroup$
    – Giskard
    Jul 15 '20 at 13:39
  • 2
    $\begingroup$ What would constitute an explanation to you? In the absence of additional information, a change in the information used to estimate expected profits, probability of costly default, the path of future discount rates, or default costs could are just some of the many reasons for the rapid change in asset prices that are consistent with the EMH. In some sense this is an impossible ask, because of the joint hypothesis problem, but even ignoring that there are numerous explanations. $\endgroup$
    – BKay
    Jul 15 '20 at 14:56
  • $\begingroup$ To let me answer in the comments: No, it does not. The EMH is not a theory that says anything about a specific price movement. $\endgroup$ Jul 15 '20 at 19:19

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