*2.1. Interpretation of Parameters.*

In both figures the values of parameters *α* and *β* are fixed. We study the effects of


Figure 1 suggests that, for *α* and *β* fixed, if a positive value of *δ* is considered then we have a unimodal distribution and the peak of the distribution increases when *δ* increases: *δ* = 0.75 (red solid line), *δ* = 1.5 (green dashed line), ..., *δ* = 3 (blue dashed dotted line). This happens for positive and negative values of *λ*.

On the other hand, in Figure 2, we have different situations. This plot suggests that, for *α* and *β* fixed, if a negative value of *δ* is considered then a bimodal distribution can be obtained. For positive *λ*, if *δ* decreases: *δ* = −0.75 (red solid line), *δ* = −1.5 (green dashed line), ..., *δ* = −3 (blue dashed dotted line), then the peaks decrease and bimodality becomes more accentuated. For negative *λ*, if *δ* decreases, then main peak increases and bimodality becomes less accentuated.

Also, note in Figures 1 and 2, that in the FBS model the pdf for negative *λ* is no longer the specular image of plot for positive *λ*.

**Figure 1.** FBS distributions for *α* = 0.75, *β* = 1 (both fixed). In (**a**) *λ* = 1 versus (**b**) *λ* = −1. Increasing values of *δ* > 0: *δ* = 0.75 (red solid line), 1.5 (green dashed line), 2.25 (black dotted line) and 3.0 (blue dashed and dotted line).

**Figure 2.** Flexible Birnbaum–Saunders (FBS) distributions for *α* = 0.30, *β* = 0.75 (both fixed). In (**a**) *λ* = 0.5 versus (**b**) *λ* = −0.5. Decreasing values of *δ* < 0: *δ* = −0.75 (red solid line), −1.5 (green dashed line), −2.25 (black dotted line) and −3.0 (blue dashed and dotted line).
