Final answer:
The exact percentage of the decline in assaults over the past decade is not provided in the references, but there has been a clear decrease in violent crimes during this period, despite public perception often thinking otherwise.
Step-by-step explanation:
The decline in assaults and other violent crimes over the past decade has not been specified exactly in percentage terms within the materials provided. To provide a precise figure, one would need relevant statistical data from a reliable source such as the Uniform Crime Reports (UCR) or the National Crime Victimization Survey (NCVR). The trend, however, is clear: both sources indicate a significant decrease in violent crime rates since the early 1990s. The public perception, nevertheless, tends to believe that crime rates are higher or worsening, a discrepancy highlighted by studies and surveys.
Given the extensive period involved and varying methodologies in studies, exact percentages of decline might differ. To fill in the blank accurately, we would need to look specifically at the period mentioned—' the past decade'—and extract data for that timeframe. Without such data in the present context, we can accurately say that violent crime, including assaults, has decreased but cannot provide a direct numerical value.