The Bottom Line:
Violent crime on O‘ahu is currently: mostly stable, but also down.
Each month, we analyze the crime data provided publicly by the Honolulu Police Department to understand crime trends and put the headlines in perspective. Currently, for each category of violent crime, we compare the number of crimes last month to the month before and the same month in the previous year. (Note that our numbers for September have changed slightly reflecting changes in the HPD Dashboard, which updates the numbers as new information is added to their system.) We do a simple statistical analysis to determine whether the year-over-year or month-to-month variation is out of the norm or expected variation. In future posts, we will offer more long-term analyses using more data. For now, our goal is a quick assessment.
If this is your first visit to the Crime Lab, check out our primer on understanding crime rates.
Aggravated Assault
There were 73 aggravated assaults in September. This is down from September 2023 when there were 96. It is also down from the number in August when there were 86.
Is this change significant? Actually, yes, some of them. The year-over-year drop from 96 to 73 is statistically significant; the month-to-month drop is not quite significant though.
Murder and Non-Negligent Homicide
There were 2 homicides in September. This is down slightly from September 2023 when there were 3. It is also down from the number in August when there were 6.
Is this change significant? No. The year-over-year drop from 3 to 2 is not statistically significant, nor is the month-to-month drop from 6 to 2.
Robbery
There were 37 robberies in September. This is down from September 2023 when there were 54. It is also down from the number in August when there were 58.
Is this change significant? Actually, yes. The year-over-year drop from 54 to 37 is statistically significant, as is the month-to-month drop from 58 to 37.
Sexual Assault
There were 61 sexual assaults in September. This is down slightly from September 2023 when there were 66. It is also down somewhat from the number in August when there were 79.
Is this change significant? Actually, yes, some of them. The year-over-year drop from 66 to 61 is not statistically significant; but the month-to-month drop of 79 to 66 is just barely statistically significant.
Looking Back and Looking Forward
Last month, we saw that although there was variation in the various counts of violent crime, aggravated assault, murder, and sexual assault were basically stable; while robbery was higher in a way that was somewhat out of the expected variation.
This month, we’re seeing that some of the variation in the counts of violent crime are significantly lower than either the previous month, the same month the previous year, or both. The exception is homicide, which continues to fluctuate within the expected variation.
It’s worth noting that robbery in particular was significantly higher in August, but significantly lower in September. This is a good reminder that the crime rate is highly stochastic, meaning it fluctuates quite a lot and we really have to look at the trend over time.
As violent crime generally was in the news so much in August and early September, seeing the counts mostly stable or somewhat decreasing can be a little surprising, but it reminds us of the importance of systematic comparison and putting specific incidences in their longer context.
Next Steps
We are just getting started with our data analysis. In the future, we hope to construct graphs to show what the trends look over time like instead of providing snapshots. We also hope to continue to pull back the curtain and discuss how we calculate the expected variation. For now, we hope our analysis provides some context.
Additionally, keep an eye out for another special look at crime in West O‘ahu as a followup to our last post putting the crime trends in statistical perspective.
Final Assessment
This month’s assessment is that violent crime on O‘ahu is mostly stable, but also down. But remember: fluctuations are to be expected and we really want to look at trends, so a future post will offer that look!
The Hawaii Crime Lab 