Reliability analysis of digital circuits is becoming an important constraint for the design process of nanoscale systems. Understanding the relations between circuit structure and its reliability allows the designer to implement tradeoffs that can improve the resulting design. In this work, we propose a method to evaluate the reliability of a circuit considering that errors below a specified threshold are acceptable. Using this new concept, named effective reliability, designers can use application-specific parameters to reevaluate the reliability of a circuit in such a way that constraints may be relaxed. In addition, we propose two metrics to calculate the effective reliability of a circuit based on bit significance and relative error rules.