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Stopping Illegal Robocalls Where They Start

Probable Cause, One State at a Time

We’re hearing more about state Attorneys General going after illegal robocallers. In many cases, an AG starts with a complaint from a constituent located in their and follows that thread via traceback.

But what if a state AG does not have specific traceback results for a call to their state. The AG might be aware of general complaints from residents about Social Security or Amazon frauds, or auto warranty scams. And they might know of traceback results implicating a particular callers and providers for such calls to other states. Does that give them reason to believe that the same perpetrators are likely calling residents of their own state?

We decided to take a look, by posing this question: If a robocaller makes X calls per day to a distribution of valid phone numbers across the country, what is the likelihood that they will call somebody in a given state?

Calculating the answer is pretty easy. To the first order, it is a function of the population of the state. California is the most populous, with almost 12% of the US population. If a robocaller dials one number from a list of valid, in-service USA numbers, they have a 12% chance of reaching somebody in California. Reaching Wyoming is far less likely; they only have 0.17% of the population. As the robocaller makes more calls, the likelihood of hitting at least one person in a given state rises quickly. If the robocaller makes just 100 calls, there’s virtually no chance of avoiding California (the probability of a hit is 99.9997%). Wyoming grows to 15.94%. Make 1,000 calls and Wyoming is up to 82.38%. Make 10,000 calls and it’s virtually certain our robocaller has called somebody in every state.

Let’s take it one step further. Suppose a robocaller decides to AVOID calling a particular state because that state’s AG is particularly tenacious about illegal robocalling. Like Wyoming, Vermont is a small state with a single area code – 802. So our robocaller avoids calling any number in area code 802, thinking he’s in the clear with Vermont’s AG.

But we know that not everybody in Vermont has an 802 phone number. There are people that moved to Vermont and kept their old number, and there are people visiting Vermont with their out-of-state phones. How many? To find out, we looked at the Federal Trade Commission’s Do-Not-Call Complaint list. FTC has over six million complaints since early 2020, each showing the location where the subject call was received, and the area code of the recipient. We calculated what fraction of the complaints in each state were reported by somebody with an out-of-state area code. This gives us a reasonably accurate indication of what fraction of that state’s population consists of “roamers” – people with a non-native area code.

Now, just like we calculated the probability of calling somebody in a given state, we can calculate how likely it is for a robocaller to reach a ROAMER in a given state. And it turns out that even if a robocaller avoids calling area code 802, if he makes 50,000 calls, there’s a 99.837% chance that he’s called somebody in Vermont. If he places 100,000 calls, it’s a virtual certainty. You can see our spreadsheet, check our math, and input your own calling values here.

So even without a specific complaint (and traceback), if a state Attorney General knows that an illegal robocaller and his voice service provider are responsible for just 100,000 calls, that AG can be reasonably certain that at least one of those calls came to the AG’s state.

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