Stack Overflow is a Q&A site where knowledge entities are presented in the form of questions and answers. Stack Overflow does not allow duplication of knowledge entities. This is enforced through a variety of methods. 

Stack Overflow's Treatment of Duplicate Knowledge Entities

Reddit is micro-blogging site that does not have a monolithic policy concerning duplicate knowledge entities. In some cases, duplication is allowed, in other cases it is not. It largely depends upon the community and moderator. 

Reddit's Treatment of Duplicate Knowledge Entities

- Stack Overflow
- Quora
- Reddit
- Wikipedia
- etc

San Jose State University

There is a significant amount of information available across various mediums such as articles, books, websites, and videos, but many of them merely repeat the existing knowledge already available in other sources, and cover the same topic. This does not mean that the media is a 100% copy of another, but the topic of the two knowledge entities is the same.

Duplicate knowledge entities in Online Communities

- Content quality control
- Limit resource cost
- Limit conflicts among users
- Protect Reputation

Why do online communities discourage generation of duplicate entries?

- Disconnected Knowledge Entities
- Stand Alone Learning Content

Causes of Dupicate Knowledge Entities in Online Communities 

Duplicate knowledge entities can be used to create an illusion of credibility, where false or misleading information is repeated enough times that it becomes accepted as true. This may create the perception of consensus and credibility around false or misleading claims. This is particularly problematic in the case of disinformation, where the intent is to intentionally deceive or manipulate an audience.

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