12.1 The Estimation (Single Prior) Approach 301 are the same as before, the bottom-right panel reveals that the difference of parameter values now straddles zero, with a difference of zero firmly in the midst of the HDI. The plot of the conjoint distribution shows why: The two parameter values are negatively correlated, such that when we believe one parameter value is large, we believe that the other parameter value is small. The negative correlation causes the conjoint distribution to straddle the line of equality. In summary, the marginal distributions of single parameters do not indicate the relationship between the parameter values. The conjoint distribution of the two parameters might have positive or negative correlation (or even a nonlin- ear dependency), and therefore the difference of the parameter values should be explicitly examined. 12.1.3 Region of Practical Equivalence (ROPE) The estimation approach can be enhanced by including a region of practical equivalence (ROPE), which indicates a small range of values that are considered to be practically equivalent to the null value for purposes of the particular