# What is EC?**Document ID:** DQ242
**Relevant to following products:** WorkOut 2.0 Manta
**Document description:** Definition: EC
EC or Effective Concentration is the concentration that leads to a percentage of the maximum effect. The software can calculate EC values (such as 20,50,80) from each fitted curve.
EC(50) is half way between the origin and the maximum effect, EC(20) is always a smaller concentration (20% effect = smaller concentration required than for 50% effect). This is regardless of the increasing or decreasing nature of the curve.
**What are the origin and the maximum effect? **
This is determined by the fit and depends on the selected fit method. For Linear Regression this is the intercept and the maximum response, for Four Parameter fit this is the lower and upper asymptotes.
**Are EC and ED the same? **
You can consider EC and ED to be the same as they are measures of the maximum effect but you must consider that the software will always calculate EC(20) to be less than EC(50), i.e. a 20% change is always before 50% change in response no matter if the curve increases or decreases. This is natural if your dose response curve is rising; the calculated EC is equivalent to the ED. However, in some environments if your dose response curve is falling you may consider that the EC values mirror ED values about EC(50), e.g. ED(20) = EC(80).
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