RESUMO O objetivo do presente estudo é investigar o efeito manada no mercado de ações brasileiro. Esse viés é bastante comum em tempos de desaceleração do mercado e pode fazer com que os investidores sofram grandes perdas. É muito difícil identificar com eficácia sua real ocorrência. Através do método de Chang et al. (2000), é possível evidenciar que a presença do comportamento de manada está associada aos seguintes fenômenos: alto volume de negócios; alta volatilidade, desaceleração do mercado; e desequilíbrio de ordens de negociação. A principal contribuição do artigo é identificar que o comportamento de manada reage assimetricamente ao sinal de choques passados. Os resultados sugerem que um movimento intenso de vendas pode gerar incerteza nos agentes, fazendo-os imitar os demais em períodos de perda iminente.

ABSTRACT The aim of the present study is to investigate herding behavior in the Brazilian stock market. This bias is quite common in times of market downturns and can cause investors to suffer large losses. It is very difficult to effectively identify its real occurrence. Through the method of Chang et al. (2000), it is possible to show that the occurrence of herd behavior is associated with the following phenomena: high trading volume; high volatility, market downturn; and misbalancing of orders. The main contribution of the paper is to identify that herding behavior reacts asymmetrically to the sign of past shocks. The results suggest that an intense selling movement can generate uncertainty in agents, causing them to imitate others in imminent loss periods.

A Berner impactor was used to collect size-differentiated aerosol samples from March to August 2003 in the city of Aveiro, on the Portuguese west coast. The samples were analysed for the main water-soluble ion species. The average concentration of sulphate, nitrate, chloride and ammonium was 6.38, 3.09, 1.67 and 1.27 µg m-3, respectively. The results show that SO4(2-) and NH4+ were consistently present in the fine fraction < 1 µm, which represents, on average, 72 and 89% of their total atmospheric concentrations, respectively. The NO3-particles were concentrated in the coarse size. Chloride presented the characteristic coarse mode for marine aerosols. During some spring/summer events, an ammonium surplus was observed (NH4+/SO4(2-) molar ratios > 2), possibly due to greater availability of ammonia coming from agricultural activities or from the neighbouring chemical industrial complex. During the remaining periods, the aerosol was found to be somewhat acidic and predominantly in the form of ammonium bisulphate (NH4+/SO4(2-) molar ratios = 0.5-1.25). Samples collected under a major or exclusive influence of maritime air masses were essentially constituted by coarse particles with enrichment in sea salt, while for air masses of continental origin the contribution of water-soluble ionic species in the fine mode was more pronounced.