Social media actors can disseminate their views about a firm, creating potential consequences for the firm. This study thus aims to explore the reaction of a firm stock market in response to the sentiments of investors on a firm's financial tweets. It focuses on the investors’ sentiments of the world's largest 100 firms’ tweets. The Naïve Bayesian classification method is used to classify sentiments of tweets into their positive and negative tones. The cumulative abnormal return and the buy-and-hold return are used as proxies for the market reactions. The study finds that positive (negative) Twitter sentiments are likely to affect positively (negatively) the market cumulative abnormal return and its buy-and-hold return. This effect is likely to hold for a shorter period and diminishes over a longer time. Besides, this effect is more associated with negative sentiments than positive ones. Further, the analysis indicates that the effect of positive (negative) sentiments is more observable in common (coded) law countries. The results suggest that Twitter sentiments carry information contents indicative of the stock market, asserting the substantial role of information on social media. The results call for establishing a direct link between social network platforms and stock markets to mitigate the panic diffusion in the market that may arise from sentiments of investors.

Purpose: The purpose of this paper is twofold. The first and the most important is to examine the efficiency of Islamic banks relative to conventional banks operating in North African Arab countries, in terms of cost and revenue efficiency. The second objective is to assess more evidence regarding the banking system efficiency trend and dynamics in each single country, and to compare such trends among countries included in the study.Design/methodology/approach: The non‐parametric data envelopment analysis (DEA) was used to estimate cost and revenue efficiency scores assuming variable returns to scale (VRS). The sample consists of nine Islamic banks and 11 conventional banks.Findings: The results indicated that Islamic banks achieved higher average revenue efficiency scores over conventional banks in this region, while the growth rate of revenue efficiency score of Islamic bank was less than conventional banks. In terms of cost efficiency, the results varied from country to another. The results also showed that both groups of banks were close to each other, with an advantage to conventional banks, which suffer less cost efficiency loss over time compared to Islamic banks.Research limitations/implications: The very limited data sources (banks' web sites) was was the main limitation faced during preparing for this research. Another limitation was the non‐regularity of annual reports.Practical implications: Islamic banks are highly challenged in finding investment opportunities/avenues that comply with Islamic regulations, unlike conventional banks that can invest in fixed income securities. There is a serious need for some countries to deregulate their banking systems more, in order to enhance the compatibility and the efficiency of their banking, such as the case of Sudan.Originality/value: Given the previously mentioned difficulties, decent data set were collected. The value of this paper is the use of nonparametric DEA to analyse cost and revenue efficiences in the countries of this region.