What are categories?
The MediaWiki software maintains tables of categories, to which any editable page can be added. To add a page to a category, include "[[Category:Category name]]" or "[[Category:Category name|Sortkey]]" in that page's wikimarkup. The categories to which a page belongs appear in a box at the bottom of the page.
Categories allow articles to be placed in one or more groups, and allow those groups to be further categorized. When an article belongs to a category, it will contain a special link to a page that describes the category. Similarly, when a sub-category belongs to a parent category, it will contain a special link to the parent category's page. Each category page contains an introduction that can be edited like an article, and an automatically generated list of links to sub-categories and articles that belong to the category. Categories do not form a strict hierarchy or tree of categories, since each article can appear in more than one category, and each category can appear in more than one parent category.
Which categories exist in the wiki?
Journal: This category assembles all single journals (for example the journal AER). For each year there is a sub-category for each journal (for example AER 2013) and for each issue of a year there is a sub-category (for example: AER 2013 (2)). In the parent category Journal you can click on each journal to open the tree of sub-categories.
Book: This category is for studies, which are published in a book.
Working paper series and blogs: This category is for studies that were published in working paper series and blogs. It is used primarily for replication studies since they are not easy to publish.
Study lacking replication: This category assembles all pages of articles which have not been replicated or have not been linked to a replication in the wiki.
Replicated study: This category is for articles which are replicated. Articles in this category have to be linked to the page of the replication in the wiki.
Replication: This category is for all articles which are replications.
Replication of more than one study: This category assembles replications, which replicate more than one original study. It is a sub-category of Replication, but studies in this category should also be in the parent category Replication.
Study with more than one replication: This category shows all studies, which were replicated more than once. It is a sub-category of Replicated study, but studies in this category should also be in the parent category Replicated study.
How do I add an article to a category?
Edit the article and add [[Category:Category name]] at the bottom of the article. For example: [[Category:Replication]] adds the page to the category Replication.
How to create a category?
Once a category is added to at least one article it automatically lists all articles it contains. It appears as a red link at the bottom of these articles until the category page itself is edited for the first time. For example, if you add a replication that was published in an issue of a journal that had not existed in the wiki before you add the category for that issue at the bottom of the replication's page. Then you click on the red link you get and add the category for the year and the journal. If that link is also red you add the category of the year to the category of the journal. If the category of the journal does not exist you write the full name of the journal on the journal category page and add the category journal.
If you add a double point a the beginning of the link to a category you will get a link but the page is not added to the category: [[:Category:Replication]] links to Category:Replication. You can also leave out the prefix: [[:Category:Replication|]] yields Replication.