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Appendix for "Making Sure You Get the Full Picture"

This page contains a more detailed explanation of two pieces of analysis that were summarized briefly in the issue Making Sure You Get the Full Picture.

Motor Vehicle Theft 

At a high level, the pattern for Motor Vehicle Theft is similar to the Breaking and Entering graph in the main article: there’s a long-term decreasing trend that doesn’t capture what’s happening with more recent data. The rate reached a minimum in 2013, then slightly increased and leveled off:

A graph of “Motor Vehicle Theft – Rate per 100,000 population” for Kitchener-Cambridge-Waterloo. The graph starts out around the 500-600 range in 1998 - 2002, then gradually decreases to a level around 150 by 2010, and stays in the 150-200 range thereafter. A blue line, nearly horizontal, has been overlaid on the years 2015-2021.

Analyzing various trend lines with different starting points confirms that the trend's direction depends on the starting year. If you start around 2011-2013, it appears to increase, but this medium-term trend seems to have stopped in recent years:

A graph of “Trend analysis results based on first year included in analysis” for “Rate per 100K population – Motor Vehicle Theft – Kitchener-Cambridge-Waterloo. It shows the “Percentage trend calculated” for each year between 1998 and 2019, inclusive. A solid blue line is surrounded by two dashed red lines. The blue line starts off around –6%, slowly increases to a value of +5% around 2012, and by 2015 is near zero. Further description is provided in the main article.

Even though the trend calculation moves negative in recent years, I'd stop short of concluding that this statistic is trending downward. The last point on the graph is based on only 4 points of data, and there is a high level of uncertainty – so concluding that this rate has been essentially flat in recent years is a more reasonable conclusion.

Robbery 

The reported rates of robberies since 1998 show significant fluctuations, alternating wildly between increases and decreases. This volatility makes year-over-year changes essentially useless for predicting future trends:

A graph of “Robbery – Rate per 100,000 population” for Kitchener-Cambridge-Waterloo. The graph jumps erratically within a range between roughly 40-90 over the time period 1998-2021.A blue line, nearly slighly decreasing, has been overlaid on the years 1998-2021.

Let’s try a trend analysis anyway to see what the results look like: 

A graph of “Trend analysis results based on first year included in analysis” for “Rate per 100K population – Robbey – Kitchener-Cambridge-Waterloo. It shows the “Percentage trend calculated” for each year between 1998 and 2019, inclusive. A solid blue line is surrounded by two dashed red lines. The blue line starts off just below 0 in 1998; in 2011 it starts increasing to a level of around 3% by 2014 but then drops sharply after that. Further description is provided in the main article.

There is a slight decreasing trend when analyzing data going back to 2004 or earlier. However, no recent point provides a reliable trend. The historical volatility is evident from the distance between the red lines: since 2007, the top red line consistently stays above 0, and the bottom error line remains below, leading to uncertainty about whether the trend is increasing or decreasing in recent years. 

A more plausible explanation is that this rate shows significant year-over-year volatility and fluctuates around a flat line. Over the 1998-2021 period, half of the time, the year-over-year change was 20% or more in either direction. This context helps us understand what changes are "normal" in this statistic when examining year-over-year data. In 2022, the rate was 61, consistent with levels seen between 2015 and 2021.

Published by:

Craig Sloss