Before revision:  Many complex interacting systems in nature , such as earthquakes , are described by power laws. In statistical physics, fluctuations for systems near the critical point follow a power law distribution. The exponents associated with the power law for fluctuations can be used to categorize the systems into specific universality classes. In economics, growth rates for firms depend on different factors for different industries .
After revision:  Many complex interacting systems in nature , such as earthquakes .