谁拥有在线媒体？
Who Owns the Online Media?
AI总结：
该研究绘制了美加欧在线新闻机构的所有权网络，发现多数机构由单一实体控制，共属同一所有权的机构报道更相似，且市场集中度多为中低水平。
AI中文摘要：
所有权对媒体的监督作用至关重要。我们绘制了美国、加拿大和欧洲数千家在线新闻机构背后的所有权网络，这些网络揭示了谁是新闻的最终责任方：超过一半的机构由单一实体控制，其余则处于多层结构背后，导致责任难以追踪。经各国可比衡量，市场集中度大多处于低到中等水平。从内容来看，我们发现共属同一所有权的新闻机构报道内容更为相似，即便在固定机构对中，随着所有权变动也是如此，尤其是在美国，人们常认为读者需求占主导地位。
英文摘要：
Ownership matters for the media's watchdog role. We map the ownership networks behind thousands of online news outlets in the U.S., Canada, and Europe. The networks reveal who is ultimately responsible for the news: for over half of the outlets, a single entity. The rest sit behind multi-layered structures, making responsibility hard to trace. Market concentration, measured comparably across countries, is largely low to moderate. Looking at content, we find that co-owned outlets report more similarly, even within fixed outlet pairs, as ownership changes -- not least in the U.S., where reader demand is often thought dominant.
