Rolling averages are used to smooth-out graphs with high-frequency noise. Since measuring the stabbings per month only gives you some 50 stabbings on average, maybe one month you’d get 30 and the next month 70 due to stochastic reasons, and so to make the graph smoother and more readable and long-term trends more visible, you can do a rolling average.
As for the “starting in 600”, that’s common practice and it’s good as long as the axes are properly labelled, which they are.
Rolling averages are used to smooth-out graphs with high-frequency noise. Since measuring the stabbings per month only gives you some 50 stabbings on average, maybe one month you’d get 30 and the next month 70 due to stochastic reasons, and so to make the graph smoother and more readable and long-term trends more visible, you can do a rolling average.
As for the “starting in 600”, that’s common practice and it’s good as long as the axes are properly labelled, which they are.