• Rule of three (medicine)
  Rule of three (medicine)
  In the statistical analysis of clinical trials, the rule of three states that if no major adverse events occurred in a group of n people, there can be 95% confidence that the chance of major adverse events is less than one in n / 3...
  
  , for calculating a confidence limit when no events have been observed
• Rule of Three (Wicca), a tenet of Wicca
• Rule of three (mathematics), a computation method in mathematics
• Rule of three (writing)
  Rule of three (writing)
  The "rule of three" is a principle in writing that suggests that things that come in threes are inherently funnier, more satisfying, or more effective than other numbers of things. The reader/audience of this form of text is also more likely to consume information if it is written in groups of...
  
  , a principle of writing
• Rule of three (play), a series of one-act plays by Agatha Christie
• Rule of three (aviation)
  Rule of three (aviation)
  The rule of three in aviation usage refers to the "3:1 rule of descent", in that 3miles of travel should be allowed for every 1000 feet descent....
  
  , a rule of descent in aviation
• Rule of three (economics)
  Rule of three (economics)
  The rule of three in Business and Economics is a rule of thumb suggesting that there are always three major competitors in any free market within any one industry. This was put forward by Bruce Henderson of the Boston Consulting Group in 1976, and has been tested by Jagdish Sheth and Rajendra...
  
  , a rule of thumb about major competitors in a free market
• Rule of three (C++ programming)
  Rule of three (C++ programming)
  The rule of three is a rule of thumb in C++ that claims that if a class defines one of the following it should probably explicitly define all three:*destructor*copy constructor*assignment operator...
  
  , a rule of thumb about class method definitions
• Rule of three (programming)
  Rule of three (programming)
  Rule of three is a code refactoring rule of thumb to decide when a replicated piece of code should be replaced by a new procedure. It states that you are allowed to copy and paste the code once, but that when the same code is replicated three times, it should be extracted into a new procedure...
  
  , a rule of thumb about code refactoring
• In survival skills, the rule of three is a rule of thumb for prioritizing needs

See also

• Rule of thirds
  Rule of thirds
  The rule of thirds is a compositional rule of thumb in visual arts such as painting, photography and design.The rule states that an image should be imagined as divided into nine equal parts by two equally-spaced horizontal lines and two equally-spaced vertical lines, and that important...
  
  , a compositional rule of thumb in photography
• Rule of thirds (diving)
  Rule of thirds (diving)
  In scuba diving, the rule of thirds is a rule of thumb that divers use to plan dives so they do not consume all the breathing gas from the diving cylinder before the end of the dive....
  
  , a rule of thumb for scuba divers