We appreciate the chance to address and correct a few points made in the article, “ShotSpotter makes up its gunfire data, but it STILL doesn’t make any sense”. The article puts forth three supposedly false claims, which we will speak to in the order they appeared:
False Claim 1 — Gunfire declined in ShotSpotter cities from 2013 to 2014
“Gunfire ‘incidents’ are never actually defined, nor are we told why this is a useful measure.”
“Added confusion stems from the complete meaninglessness of ‘total rounds per incident’ and how this relates to ‘average rounds.’”

We did not define the term ‘incident’ in our First Half 2014 Gunfire Index. However, the definition of ‘incident’ it is made perfectly clear in our 2013 Full Year Index. An ‘incident’ is one or more gunshots (multiple rounds) that have been detected by ShotSpotter and, based on time and location, can reasonably be grouped into a single incident. To see the Full Year 2013 index, go here.

As the most complete source of gunfire data in cities where ShotSpotter is deployed, we can state for certain that incidents of gunfire definitely *did* decrease, significantly, by 20.6% from 14,703 in 31 communities monitored by ShotSpotter in 1H2013 compared to 11,675 in the same 31 communities in 1H2014.

Furthermore, the ‘total rounds per incident’ is the total number of gunshots (bullets fired) detected by ShotSpotter in the coverage area we’re analyzing. The ‘average rounds’ is the average of gunshots per incident. The average adjusts for the change in the number of incidents. Both numbers are used because they measure different things –
 The ‘number of incidents’ is a reflection of the number of gun-related crimes.
 The ‘number of rounds per incident’ provides and indication of the overall intensity of multiple round shooting event and to some degree the use of higher capacity firearms.

“This makes it pretty clear that the “incidents” measure is here to obscure the fact that gunfire increased by 36% in the 31 ShotSpotter communities during the period of the study. … Far from reducing gun violence, its figures suggest it has aggravated gun violence in the communities where it is deployed.”

With the understanding above of differentiating incidents from rounds fired, you see the data showed that, while the average ShotSpotter community saw a 20.6% decrease, some police agencies and their respective cities saw much greater decreases of 40%, 50% and more. The maximum reduction we saw year-on-year was in Springfield, Massachusetts, where gunfire incidents decreased by 60% from 1H2013 to 1H2014.

False Claim 2 — SpotShotter is responsible for reducing gun violence
Correlation, causation and the “clear implication that ShotSpotter made this happen.”
“… correlation is not causation.”

ShotSpotter does not claim that we are exclusively and directly responsible for any decrease in gunfire incidents. But this cause-and-effect problem occurs for all crime-reduction efforts. There is no conclusive proof that can measure the direct result of any one specific, isolated, crime-fighting program or technology. Most of the agencies we work with combine several approaches into a comprehensive and proactive program to bring about a reduction in crime. We believe the most powerful attribute in reducing gun crime is community collaboration and cooperation with public safety agencies that have earned the trust in those communities. That trust is earned by providing higher levels of targeted responsiveness and service around gun crime that we know happens much more frequently than gets reported to police. We do believe very much that we help enable that process when our technology is combined with agency best practices and other gun crime reduction efforts.

False Claim 3 — ShotSpotter bases its claims on real-world data
The 14,703 gunfire incidents in 1H2013, and the 11,675 gunfire incidents in 1H2014 are an aggregation of our own database of actual shots fired in our ShotSpotter-covered areas. We have collected, analyzed and confirmed each of those incidents with both an audio and a visual review, before publishing out to the local law enforcement agency. That’s what we would refer to as ‘real world data.’

“The supporting graphic (Web version[5]) both hides the high number …”
“Bizarrely, this most basic claim, the one politicians and media picked up on, is proved false (or unintelligible) by ShotSpotter’s own figures.”

Nothing is hidden. All of the numbers are presented the same way in the graphics and in the text. The Index highlighted the bad news of the increase in the number of rounds per incident the same way it highlighted the good news of the drop in the number of incidents.

“… it comes as a surprise that ShotSpotter actually made up data to fill out gaps in its observed gunfire tracking.”
“So, in other words, up to 45% of any particular community’s data over a six month period was ‘imputed’ by means of this process of ‘proration.’”

Your writer shows a lack of understanding of basic statistical imputation.
 Missing data arise in almost all serious statistical analyses , and imputation is a standard and accepted technique for filling in missing data in a statistical analysis. It is similar to a seasonal adjustment. It was used for those communities that did not have full coverage over our comparison period. If, for example, a community started using ShotSpotter starting on February 1, 2013, we will be comparing 5 months of 2013 to 6 months of 2014. We must deal with the missing data from January 2013.
 If we simply take the averages, we are making the hidden assumption that January 2013 is the same as the average of the rest of 2013. But we know that the missing month does not necessarily look like the other 5 months due to seasonal variation. Imputation takes other information from all the rest of our data into account to make a more intelligent estimate for January. We did not “make up data”, and MOST importantly, we were very clear and transparent in footnoting the fact that we did use imputation.

Those are the facts. We are a company that strives for perfection and are passionate about helping make a real difference in the public safety posture of many underserved communities while being commercially viable. We are open to having dialogue about the facts of what we do but are concerned when we see people or organizations purposely miss state and/or miss lead those facts. Our hope is that your blog posting was done hastily and led to conclusions based on misunderstandings versus intentional misdirection.

Thank you in advance for publishing our rebuttal.

SST, Inc.