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A Inteligência Artificial (IA) tornou-se um dos principais impulsionadores de valorização das grandes empresas tecnológicas, influenciando expectativas de inovação, crescimento e competitividade. Nos últimos anos, as “Sete Magníficas” — Apple, Microsoft, Alphabet, Amazon, Meta, Nvidia e Tesla — realizaram diversos anúncios de IA, gerando movimentos relevantes nos mercados financeiros e estimulando a investigação académica sobre a forma como este tipo de informação é incorporada nos preços das ações. O principal objetivo deste estudo consistiu em analisar se os anúncios de IA destas empresas originam retornos anormais e se a reação dos investidores é consistente com a hipótese de eficiência semi-forte dos mercados financeiros. Para tal, foi aplicada a metodologia de Estudo de Eventos, com dados diários entre 2021 e 2024, de forma a avaliar o comportamento das ações em diferentes janelas de evento. O retorno esperado foi estimado através do modelo CAPM e do modelo de cinco fatores de Fama-French. Os resultados indicam que os anúncios de IA não geram, de forma sistemática, retornos anormais persistentes, embora determinados anúncios produzam reações imediatas dos investidores. Verifica-se ainda que a reação do mercado varia em função da natureza dos anúncios, enquanto a evidência de efeitos de contágio é limitada. Em termos gerais, os resultados obtidos são consistentes com a hipótese de eficiência semi-forte dos mercados e contribuem para a literatura sobre eficiência dos mercados e sobre o impacto económico e financeiro da IA.
Artificial Intelligence (AI) has become one of the main drivers of the valuation of major technology companies, influencing expectations regarding innovation, growth, and competitiveness. In recent years, the "Magnificent Seven" — Apple, Microsoft, Alphabet, Amazon, Meta, Nvidia, and Tesla — have made several AI-related announcements, generating significant movements in financial markets and stimulating academic research on how this type of information is incorporated into stock prices. The main objective of this study was to analyse whether AI announcements made by these companies generate abnormal returns and whether investors' reactions are consistent with the semi-strong form of the Efficient Market Hypothesis (EMH). To this end, the Event Study methodology was applied using daily data from 2021 to 2024 in order to evaluate stock price behaviour across different event windows. Expected returns were estimated using the CAPM and the Fama-French five-factor model. The results indicate that AI announcements do not systematically generate persistent abnormal returns, although certain announcements produce immediate investor reactions. The findings also show that market reactions vary according to the nature of the announcements, while evidence of contagion effects is limited. Overall, the results are consistent with the semi-strong form of market efficiency and contribute to the literature on market efficiency and the economic and financial impact of AI.
Artificial Intelligence (AI) has become one of the main drivers of the valuation of major technology companies, influencing expectations regarding innovation, growth, and competitiveness. In recent years, the "Magnificent Seven" — Apple, Microsoft, Alphabet, Amazon, Meta, Nvidia, and Tesla — have made several AI-related announcements, generating significant movements in financial markets and stimulating academic research on how this type of information is incorporated into stock prices. The main objective of this study was to analyse whether AI announcements made by these companies generate abnormal returns and whether investors' reactions are consistent with the semi-strong form of the Efficient Market Hypothesis (EMH). To this end, the Event Study methodology was applied using daily data from 2021 to 2024 in order to evaluate stock price behaviour across different event windows. Expected returns were estimated using the CAPM and the Fama-French five-factor model. The results indicate that AI announcements do not systematically generate persistent abnormal returns, although certain announcements produce immediate investor reactions. The findings also show that market reactions vary according to the nature of the announcements, while evidence of contagion effects is limited. Overall, the results are consistent with the semi-strong form of market efficiency and contribute to the literature on market efficiency and the economic and financial impact of AI.
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Estudo de eventos Inteligência Artificial Sete Magníficas Retornos Anormais Hipótese dos Mercados Eficientes Event Study Artificial Intelligence Magnificent Seven Abnormal Returns Efficient Market Hypothesis