sudden-change

You have identified your process as involving:

✓ change(rather than no change), which is
✓ sudden(rather than smooth).

This implies that you expect certain aspects of the process—such as the mean, variance, and/or dynamics—to transform abruptly over time.

Follow-up question:

Is the sudden change lasting or reversible?

sudden lasting change

Transformation occurs abruptly over time and is persistent. Hence, if the mean changes, there is either an upward or downward shift. Similarly, when the variance and/or dynamics change, they change in a certain direction (i.e., increase or decrease), and do not revert back.

sudden reversible change

Transformation occurs abruptly over time and is transient. Hence, if the mean changes, there are upward as well as downward shifts. Similarly, when the variance and/or dynamics change, the shift is in a certain direction and is (partly or fully) reversed after some time.

I think my process involves:

sudden lasting change sudden reversible change

Not sure?

When you theorize about the process you are interested in, you may realize that the temporal lens that you adopt in your study plays an important role in whether changes will show up as reversible or not. When the time span of your study is limited, or only little detail is obtained, change may appear lasting; in contrast, when the time span of your study or the resolution of your measurements increases, change may show up as reversible. Hence, to decide whether models for reversible change or models for lasting change are most relevant for the process you want to study, you have to consider the temporal design of your study.

When you look at empirical patterns in your intensive longitudinal measurements and you see a sudden increase followed by a sudden decrease (or vice versa), it is clear that the change in the process is reversible. However, when you see sudden change only in one direction (e.g., an increase in the mean, or a decrease in variability), this does not imply that change will also show up as lasting if you were to adopt a different temporal lens based on a different temporal design.

When you are unsure whether the process is characterized by lasting or reversible change, you are advised to continue with both options to get a better overview of the various modeling possibilities.