Mostrar código-fonte de Sobre reacção

'''Sobre reacção''' / '''Reacção exagerada''' (em inglês, overreaction), é a tendência que parece existir de os activos exagerarem os movimentos devidos a um padrão consistente de notícias positivas ou negativas. 

Esta tendência parece em contradição com o [[enviesamento conservador]], mas na prática está relacionado. O enviesamento conservador faz-se sentir no curto prazo, onde os papéis tendem a não descontar totalmente o efeito de novidades fundamentais. Isso leva a que se estabeleçam tendências no sentido dessas novidades fundamentais (surpresas negativas criam tendências negativas, surpresas positivas criam tendências positivas). O que acontece de seguida é que essas tendências acabam por ir longe demais, dando origem à reacção exagerada no longo prazo. As tendências positivas levam a uma subida exagerada pelo que são invertidas, as tendências negativas levam a uma descida exagerada pelo que também são invertidas. 

Resumindo, no curto prazo existe uma subreacção a novidades fundamentais, que leva a uma tendência no sentido destas, que leva a uma sobrereacção a novidades fundamentais.


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