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This paper examines how CEO overconfidence affects the tone of press releases. Using option‐based proxies for CEO overconfidence, I find that over the 2000–2018 period, the press releases issued by firms with overconfident CEOs have more positive tone and receive more positive market reactions. The relation between CEO overconfidence and the tone of press releases is stronger among firms with good operating performance and concentrated in investment‐related news but is insignificant for earnings news. These findings suggest that CEO overconfidence leads to biases in press releases.

摘 要 为明确围栏封育对温带典型草原群落物种种间关系的影响, 运用方差比率法、基于2 × 2列联表的χ 2 检验、Ochiai指 数、Spearman相关分析, 对位于内蒙古锡林郭勒盟太仆寺旗封育6年的围封样地及围栏外样地的主要优势种及伴生种进行了 种间关联和相关性分析。同时运用生态位宽度指数分析围栏内外物种对环境资源的利用能力及种间竞争情况。结果表明: 1) 基于2 × 2列联表的χ 2 检验结果表明围栏内9个种对显著正联结, 4个种对显著负联结(p ≤ 0.05), 围栏外有19个种对显著正联 结, 8个种对显著负联结; Spearman秩相关分析表明围栏内有10个种对显著正相关, 16个种对显著负相关, 围栏外有12个种对 显著正相关, 30个种对显著负相关。 χ 2 检验和Spearman检验结果表明围栏内群落处于稳定发展状态, 而围栏外群落处于退化阶 段。 2)围栏内外的优势种Ochiai指数都较高, 但χ 2 检验并不显著, 表明优势种之间的关联程度高, 但存在相对独立的分布格局。

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