Identifying sustained change
A sustained change is one that lasts for the longer term. Identifying whether a behavioural change has been sustained needs to be done with repeated measures over time.
Figure 7 shows a change in the relationship between the compliance behaviour and the comparison statistic that corresponds with the treatment period. The 2008-09 observation indicates that the new relationship is holding.
If the behavioural change is sustained, you would expect to see the paths of the two groups continuing to track in parallel over an extended period of time as seen in figure 8.
Tracking the behaviour for a short period after the intervention will not always give a reliable indication of whether the effect is sustainable over time - as figure 9 illustrates, while the behaviour is tracking in parallel with the comparison statistic in the 2008-09 income year, the slight decline in compliance behaviour continued. The declining behaviour was originally masked by changes in the environment. Looking at the pattern of observations over a longer period clearly shows that the effect of the strategies was short-lived and not sustained.
There is no set period of time over which you should track your data to identify whether a change is sustainable. However, you will need to track behaviour for several years to really understand whether your strategies have had a lasting impact.