In the middle of a Tuesday afternoon last December, a shootout erupted at a busy intersection in the Mid-City neighborhood of New Orleans. Nearly 50 rounds were fired, riddling several cars with bullets, yet only one person was hit; the man sustained a leg injury that was not life-threatening.

A year and a half before, in September 2013, an all too similar gunfight took place around midnight in the city’s Carrollton neighborhood. This time, a bullet pierced a nearby home, striking and killing an 11-year-old girl.

These two unrelated cases in one of the country’s worst cities for gun violence can help us understand why murder statistics alone are a bad metric for measuring gun violence trends. Both featured groups of gunmen firing wildly in the vicinity of innocent bystanders, but only one ended in a tragedy receiving extended public attention. So even though 90 percent of New Orleans murders are committed with a gun, looking at total shooting incidents tells us more — by focusing attention on all the gun violence in a city, in addition to those shootings that end in a fatality. The open data movement is making it possible to evaluate thousands of shooting incidents and develop analytic insights into gun violence’s big picture. These conclusions in turn can help us evaluate the effectiveness of programs seeking to reduce gun violence.

Any shooting can become a tragedy for the victims and their families, but my analysis of thousands of incidents in two cities over several years suggests that whether an individual shooting ends in a fatality is largely random. There can be a number of factors — the distance between shooter and victim, the number of bullets fired, the shooter’s age and experience with a firearm, the amount of daylight/moonlight, etc. — that influence whether a shooting incident is fatal or not. This randomness can be the difference between a rain of bullets hitting one person in the leg or killing a young girl in her bed.

Over time, the percentage of shootings that end in a fatality will be fairly stable, although the level may vary from city to city. Short-term variations above or below a city’s typical fatal shooting ratio could be attributed to any number of factors, but there’s no evidence that the ratio varies significantly over the longer term, at least in the last six years. Understanding this concept can help explain whether gun deaths in a city are rising or falling because of chance or if a change is due to increasing or decreasing gun violence.

It is virtually impossible to figure out shooting incident totals for a city using the Uniform Crime Reporting Program, a system run by the FBI to help police departments across the country track patterns in violent crime and property crime. Although the system does provide a repository for comparing crime trends throughout the country, it has a few shortcomings: Publicly available UCR statistics count victims rather than incidents, they do not differentiate between murders by firearm and those with other causes, and they count all aggravated assaults the same regardless of what weapon was used.

But a few cities — particularly New Orleans and Baltimore — organize their publicly available crime data in such a way as to make tabulation of shooting incidents possible. These cities have historically been two of the country’s most violent and are good models for understanding urban gun violence.

New Orleans

New Orleans was one of the country’s deadliest cities in 2012, when it began a program of focused deterrence against known gang members. Largely as a result, the city saw a 22 percent drop in murders, from 199 in 2011 to 156 in 2013. The murder count in New Orleans fell again in 2014, by about 4 percent. Although murder is a flawed statistic, I will use it as a barometer here because the FBI and cities throughout the country almost exclusively use it when talking about changing gun violence patterns.

But after three consecutive years of murder reduction, New Orleans is experiencing a rising murder total in 2015. There were 132 murders counted by the city police in New Orleans through September, the latest full month of available data, compared with just 114 murders over the same period in 2014 and 112 in 2013.

Solely looking at these numbers suggests that New Orleans is undergoing a considerable rise in gun violence in 2015. But analyzing the city’s publicly available data on all shootings establishes an alternative narrative.

In New Orleans since 2010, there have been more than 2,400 shootings in which a person was hit. Of those incidents, 36 percent resulted in at least one death.

There were 70 more shooting incidents in New Orleans in 2014 than in 2013, but less than 32 percent of shootings in 2014 led to a fatality, compared with 36 percent in 2013. So New Orleans experienced a slight drop in the murder count last year, largely because the fatal shooting ratio fell.

Conversely, New Orleans was on pace for 25 fewer shooting incidents in 2015 than in 2014 as of the end of September but may see a rise in the number of murders this year because nearly 40 percent of shooting incidents are ending in at least one fatality.

You might say that New Orleans was due for a rise in the murder count in 2015 simply because of the randomness in fatal shootings the city experienced in 2014. Alternatively, the city may be due for a fall in the number of murders in 2016 presuming overall shooting levels remain below where they were from 2010 to 2012.

Baltimore

A similar analysis can be conducted on gun violence in Baltimore. The city’s open data system is structured a little differently from the one in New Orleans, but it is possible to establish the number of shootings and number of fatal shootings there since the beginning of 2010 relatively accurately. Baltimore’s data is also up to date through September of this year.

Around 34 percent of nearly 3,000 shooting incidents in Baltimore since 2010 have ended in a fatality. Baltimore is on pace for a large jump in the number of murders this year, however, because the city is seeing 60 percent more shootings in 2015 than in 2014. While New Orleans appears to be experiencing a change in luck, Baltimore is experiencing a dramatic jump in gun violence.

Looking more closely at 2015 highlights the spike in gun violence in Baltimore that began in late April and its gradual slowing since the end of July. Despite this slowing, there were still more shooting incidents in September than there were in any month from 2010 to 2014.

Few cities structure their open data portals sufficiently to allow for isolating shootings in this manner. Focusing on shootings, rather than murder, can lead to a much richer understanding of gun violence trends and help the public understand the “why” behind changing crime trends. Cities might consider setting reductions in shooting incidents (in addition to lowering the murder rate) as a metric of success and focus their open data resources on enabling residents to truly evaluate gun violence patterns as Baltimore and New Orleans have done.