Research:What is the minimal healthy community size?

This question set is among the high level research priorities for the Wikimedia Summer of Research 2011. The full list is here, and this is categorized as "RQ10".

Numerous studies show that (the English) Wikipedia is no longer growing at the rates it used to grow. Along certain dimensions, there is even decline. For example, the number of active editors and new wikipedians is slowly declining. This means that a larger workload has to be carried out by a smaller group of volunteers. This overall research question tries to answer how large the community should be at a minimum to ensure quality of content and fighting vandalism.

Workload Edit

(RQ10.1) How many editors does it take to guard the quality of a single article?

(RQ10.2) How many editors does it take to fight vandalism?

(RQ10.3) How big is the difference in minimum healthy community size between a community focussed in one time zone such as Tamil, Afrikaans, Navaho or Swedish and one like English where it is always school playtime somewhere in the world?

(RQ10.4) How much editing activity is needed to maintain the existing articles on a Wikipedia? - Example EN Wiki has circa 500,000 Biographies of Living People, more than 10,000 of whom die every year.

(RQ10.5) How much editing activity is needed to maintain the coverage of a Wikipedia? - Example The Olympics comes round every 4 years as do several countries general elections plus the Oscars and assorted natural disasters. To maintain coverage of these areas not only do some existing articles need to be maintained but many entirely new ones need to be created.

(RQ10.6) Does minimum size correlate with scope? So a wiki focussed on one author might be viable with half a dozen editors, but a general wikipedia could have dozens of editors who only ever collaborated on rare occasions such as when a notable ballerina goes into Politics.

Psychology Edit

(RQ10.7) What are the early signs of community decline?

(RQ10.8) Is community decline self reinforcing?

(RQ10.9) Is community decline a gentle measured process or are there tipping points that can lead to step change decline?

(RQ10.10) When communities bounce back with an influx of new editors, do the old guard get reinvigorated and return? If so what are the things that help different wikigenerations to integrate, and what drives them apart?

(RQ10.11) Are there different types of editors in terms of their need for different levels of community interaction? If so do the less social editors drift away when a site becomes too busy for them? and if so do they return after things calm down?

(RQ10.12) How does the hierarchy of userights affect this, do expectations for adminship tend to stabilise (symptom almost everyone's an admin and things can seem quite cliquey) or do editors get ever pickier as to who they support for adminship and eventually it becomes a de facto clique that newer editors see as always out of reach.

Models Edit

Which of the following models have a best fit to actual community dynamics and need for editors.

(RQ10.13) The number of watchers on the walls is limited, so the best strategy is to tighten the perimeter and reduce what is inside (the deletionist paradigm). - Health means rising average quality.

(RQ10.14) The number of watchers on the walls depends on the amount we protect, so the more we extend what is allowed inside the more easily we can protect the perimeter, (the inclusionist paradigm). Health means growth.

(RQ10.15) The amount of contents is irrelevant, the key metric is the efficiency with which our trusted users can check and correct, approve or revert the changes taking place. Health is measured in the speed with which vandalism is reverted.