In meta-analysis, which term refers specifically to the absence of an effect?

In meta-analysis, the term that specifically refers to the absence of an effect is the "line of no effect." This concept is crucial in visual interpretations of meta-analysis results, particularly in forest plots. The line of no effect typically represents a value where the treatment or intervention has no impact compared to a control or alternative group. For example, in studies assessing risk ratios, the line of no effect would be at a risk ratio of 1; for differences in means, it would be at 0. If the confidence intervals of the studies included in the meta-analysis intersect this line, it indicates that no statistically significant difference exists between the groups being compared.

The other terms, while related to outcomes in research, do not specifically signify the absence of an effect in the same precise way. The term "no significant effect" generally describes a result that does not achieve statistical significance but does not clearly indicate where the line is drawn. "Line of equality" is often used in the context of comparing two variables but does not directly address the concept of no effect. Lastly, "neutral outcome" might describe a situation with no beneficial or harmful effects, but it isn't the standardized terminology used in statistics to depict the absence of an effect in meta-analysis.