Phillip Levine is the Katharine Coman and A. Barton Hepburn Professor of Economics at Wellesley College and a research associate at the National Bureau of Economic Research. Robin McKnight is professor of economics at Wellesley College and a research associate at the National Bureau of Economic Research. The views expressed in this commentary are their own. View more opinion on CNN.

(CNN) With Thursday's one-year anniversary of the Parkland shooting that gripped America's attention, Democrats are reintroducing a bill to ban high-capacity gun magazines. If history is any guide and this bill garners substantive support, the debate over that measure -- like the discussions after shootings at Parkland, Sandy Hook and San Bernardino -- could increase gun sales.

What distinguishes these three shootings from the others is the prolonged national media attention and changes in public opinion that occurred regarding gun control. In the past , we have argued that the national attention that drove the prior surges in gun sales resulted from specific national policy proposals , including background checks on all gun sales and assault weapons bans. What we learn from Parkland is that a grassroots movement successful in generating national attention also leads to such a spike, even in the absence of significant policy actions.

According to our analysis, 600,000 additional guns were sold between February and April 2018 -- beyond the 6.7 million that would have been expected otherwise over that period. Sandy Hook and San Bernardino generated an additional 3 million and 1.7 million additional guns, respectively, sold in the few months after those shootings.

Fear of gun control is a powerful determinant of gun sales; that fear is stoked when a mass shooting receives tremendous national attention. Mass shootings tend to receive that attention, but it typically lasts for just a few days. President Barack Obama extended the focus after Sandy Hook and San Bernardino by proposing specific new national gun control regulations.

Parkland was different. After briefly indicating support to "get something done" after the Parkland shooting, President Donald Trump reiterated his strong support for gun rights. With Republicans controlling both houses of Congress at the time, there was no reason to expect any substantive national gun control legislation.

If the prospect of meaningful national gun control legislation is the factor driving spikes in gun sales, we should not have seen one after Parkland. So, why did one occur?

One potential explanation is that a new focus on state gun control legislation drove the increase in gun sales. Indeed, Parkland did generate many new laws at the state level, which may have contributed to greater concern about restrictions on gun access. In total, 25 states enacted new gun control laws in the six months after the shooting. Six states (Florida, Oregon, South Dakota, Utah, Washington and Wisconsin) did so in March of 2018, within weeks of the shooting.

Yet our analysis shows that these state laws did not drive the spike in gun sales. One may have expected the six states quickly implementing new laws to experience larger spikes in gun sales relative to the rest of the country, but they did not. For instance, the percentage change in gun sales between March 2017 and March 2018 in Florida, where legislation was enacted, was no larger than neighboring Georgia with no law change, or even compared to the national average.

These laws may have had little impact on gun sales, precisely because they were not intended to have a broad impact. The types of laws passed are highly targeted at reducing gun access among very specific types of potential offenses ( domestic violence ) or offenders ( the mentally ill ). It is unknown whether these laws have the precision necessary to get the job done, but they largely do not affect gun availability for the broader public.

A more plausible explanation, suggested by Parkland, is that public attention may remain on gun control over a prolonged period, even if there is no substantive national gun control legislation pending. After Sandy Hook and San Bernardino, the formal gun control debates started by Obama accomplished that. After Parkland, students, such as Emma Gonzalez and David Hogg, were successful in keeping the story in the news for an extended period. The March for Our Lives on March 24, about six weeks after the Parkland shooting, helped as well. Past analyses document the lengthier media coverage devoted to Parkland compared to other infamous mass shootings.

That national attention may have generated fear among gun rights advocates despite the lack of national legislative interest. That fear may not have matched the level after Sandy Hook and San Bernardino, which did generate national legislative interest, but it did occur. Indeed, national polls after Parkland showed rising popular support for stricter gun laws. And our analysis shows that the states where gun sales rose the most after Parkland are the states where Obama received the lowest electoral support in 2012. These states have the highest gun sales and represent the locations where fear would most likely translate to greater gun purchases.

Spikes in gun sales can have dangerous consequences. Our past research shows that the large influx of newly purchased weapons leads to more accidental deaths. Those guns are more likely to be stored improperly and handled by their new owners, potentially resulting in accidental discharge. We found that around 60 people were killed this way in the few months after Sandy Hook.

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What can we learn from all this -- if our goal is to reduce gun-related injuries? Any substantive, national discussion of gun control is likely to increase gun sales, at least in the short run. The more serious the discussion, the greater the increase in sales. And the greater the increase in sales, the more accidental deaths may result.

This conclusion should not be misconstrued as suggesting policymakers avoid proposing restrictions on guns. Rather, policymakers should seek to minimize the short-term consequences associated with such proposals. The most effective gun control discussions are those that translate into bold policy proposals that are enacted rapidly.

A proposal to ban assault weapons, for instance, would be more effective if it is enacted quickly, rather than after lengthy debate, to minimize the unintended consequences from spikes in sales. Of course, with Republicans in control of the White House and the Senate, the current proposal to ban high-capacity gun magazines is unlikely to receive the necessary political support to turn policy into law.