CAPM: an absurd model

Pablo Fernandez (http://web.iese.edu/PabloFernandez/), CAPM: an absurd model, (download: http://ssrn.com/abstract=2505597)

ABSTRACT. The CAPM is an absurd[1] model because its assumptions and its predictions/conclusions have no basis in the real world. The use of CAPM is also a source of litigation: many professors, lawyers… get nice fees because many professionals use CAPM instead of common sense to calculate the required return to equity. Users of the CAPM make many illogical errors valuing companies, accepting/rejecting investment projects, evaluating fund performance, pricing goods and services in regulated markets, calculating value creation…

According to the dictionary, a theory is “an idea or set of ideas that is intended to explain facts or events”;and a model is“a set of ideas and numbers that describe the past, present, or future state of something”. With the vast amount of information and research that we have, it is quite clear that the CAPM is neither a theory nor a model because it does not “explain facts or events”,nor does it“describe the past, present, or future state of something”.

It is important to differentiate between a fact(something that truly exists or happens: something that has actual existence; a true piece of information)and an opinion(what someone thinks about a particular thing).The CAPM could be described as anuninformed opinion,and not as asensible opinion.

We all should try to explain a portion of “the world as it is”, not of “the world according to a wrong theory” nor of “the world if men were not men”. Ricardo Yepes, professor of philosophy of my university, wrote: “Learning means being able to keep perceiving reality as it truly is: complex – and not trying to fit every new experience into a closed and pre-conceived notion or overall scheme”.

We may find out an investor’s expected IBM beta and expected market risk premium (MRP) by asking him. However, it is impossible to determine the expected IBM beta and the expected MRP of the market (for the market as a whole), because these two parameters do not exist. Different investors have different cash flow expectations and use different expected (and required) returns to equity (different expected market risk premium and different expected beta). One could only talk of the beta and the market risk premium if all investors had the same expectations. But investors do not have homogeneous expectations.

Sections 11 and 12 show how to calculate required returns in a sensible way and how to use betas being a reasonable person.

  1. Main assumptions of the CAPM                                 2. Main predictions of the CAPM
  2. Why CAPM is an absurd model?                                4. Why many people still are using CAPM?
  3. Schizophrenic approach to valuation                       6. Consequences of using the CAPM
  4. Papers about the CAPM                                              8. Problems with calculated betas
  5. Problems calculating the Market Risk Premium  10. Expected, required and historical parameters
  6. How to calculate required returns?                         12. How to use betas and to be a reasonable person
  7. Conclusion
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2 commenti

  1. Inviato ottobre 8, 2014 alle 5:29 pm | Permalink | Rispondi

    I dubbi e le vere e proprie critiche al modello capm e alla teoria del portafoglio cominciarono ad arrivare già in occasione dell crash del 1987 e continuarono ininterrotte anche dopo il conferimento del nobel ai suoi fondatori e fino al clamoroso fallimento-salvataggio del LTCM . ecc. Memorabile la critica feroce al fondamento gaussino del modello lanciata da Taleb bel suo bestseller The black swan. Chissà se il modello gode del successo di una volta nelle università americane e non.

    Mi piace

    • Inviato ottobre 10, 2014 alle 9:21 am | Permalink | Rispondi

      Non tutti lo sanno, però… dato che anche nel nostro Ateneo, invece che cassare l’argomento, se ne parla ancora… Ma forse non hanno ancora letto il lavoro di Taleb.

      Mi piace

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