Category: News

The useleness of absolute numbers

A few days ago, I was reading an article about accidents involving cyclists. Being an avid cyclist and dealing with data and numbers of all kinds every day, I immediately noticed this sentence: “The regions most affected by accidents are those where bicycles are a real tradition: Lombardy, Veneto, Emilia Romagna, and Tuscany. Incidents tend to occur on Saturdays and Sundays, between 10 AM and 12 PM, during the months of May to October, with a peak in August.”

What seems odd to you?

After reflecting for a moment, it’s clear that the regions, days, and times when accidents are most frequent are simply those when cyclists are most frequently on the road. This is a type of error or oversight that’s fairly common among journalists, who, being less familiar with numbers, often report data without critically analyzing it.

Saying that accidents happen more frequently on Saturdays and Sundays doesn’t provide any useful information, because those are the two days when cyclists are on the roads the most, and thus are also the days with the highest risk of accidents (the same logic applies to the most popular months and times of day). In this case, the raw data doesn’t make any sense unless it’s somehow “cleaned up.”

What needs to be done in such cases is to have a “benchmark” to compare the results (what’s referred to as a “benchmark” in English). In the case of our article, a simple benchmark could be the ratio between the number of accidents and the number of cyclists on the road that day. This means that, instead of looking at the absolute number of accidents, we look at the relative number. By doing this, we give each day of the week the same “probability” of being the most dangerous day, removing the natural advantage that days like Saturday or Sunday have due to the higher number of cyclists.

Let’s take a look at the table below (note that the numbers are fictional):

DayNumber of accidentsNumber of cyclistsRatio
Mon101.0001,0%
Tue152.0000,8%
Wed101.5000,7%
Thu151.0001,5%
Fri203.0000,7%
Sat408.0000,5%
Sun6010.0000,6%

If we consider the absolute number of accidents, Sunday is the most dangerous day with 60 accidents. However, if we use the correct benchmark, dividing the number of accidents by the number of cyclists on the road, the most dangerous day in relative terms becomes Thursday, with a ratio of 1.5%.

A similar example of this concept is found in marketing: the effectiveness of an advertising campaign targeted at a certain group of people is evaluated not only by looking at the absolute value, but by comparing it to the results of a “control group” – a group of customers who are not exposed to the campaign. Only by “relativizing” the absolute results can we determine whether the campaign was effective or not.

So, when you come across statistics and conclusions like this, pay attention to the data and ask yourself whether they’ve been properly analyzed or not, because otherwise, they might not make any sense.

And anyway, to stay safe and avoid articles like this, when you go out cycling, be careful around cars!

A statistical approach to terrorism

Datastory.it is also about current events, and following the attacks in Paris, we want to share our opinion on the matter.

The series of attacks that struck the French capital on November 13, 2015, seems to have shaken public opinion and mobilized European governments. In newspapers, parliaments, and international forums, the primary focus is how to ensure safety and prevent the horrific events in Paris from happening again. Many hypotheses are being considered: stricter border controls, revising the Schengen Agreement, increased surveillance in high-risk areas, and the installation of cameras in major cities.

Additionally, there are discussions about allocating more personnel and resources to security (the press mentions €400 million in Belgium, €120 million in Italy). And then there are the bombings in Iraq and Syria, with the United States, Russia, and France taking the lead. Some estimates suggest the U.S. spends $10 million daily on these operations, while Russia spends about a third of that amount.

The caliphate in Iraq and Syria is undoubtedly a threat to the Western world. More broadly, in recent years, Islamist terrorism has caused deaths and suffering even in Europe.

From the Madrid bombings on March 11, 2004, to the Paris attacks on November 13, 2015, 411 people have died in seven Islamist terrorist attacks. The number rises to 488 if we include the July 22, 2011, attack in Norway by Breivik (which had an anti-Islamic motivation).

But how much does it cost us to protect ourselves from terrorist attacks? How far are we willing to go to prevent more lives from being lost to fanatics killing in the name of their religion?

And in a world where resources are limited, what are we willing to give up to increase our security?

Let’s reflect on these questions using some concrete examples. In Italy alone, around 1,000 people die each year in workplace accidents (source: Osservatorio sui morti del lavoro), 3,385 people in road accidents (2013, source: ISTAT), 12,004 women from breast cancer (2012, source: ISTAT), and an astonishing 83,000 deaths are attributable to smoking!

How many lives could be saved if the significant resources budgeted for defense against terrorist attacks were instead used for anti-smoking campaigns? If millions were invested in securing the road network and law enforcement increased traffic and alcohol checks? How many of the 12,000 women who die each year from breast cancer could be saved if we doubled free mammograms?

It’s difficult to answer these questions (though we will delve deeper into this topic), but let’s make a few assumptions. Let’s take the €120 million the government has declared it will allocate to protect us from terrorist attacks following the Paris events. We could decide to allocate them in three different ways, as outlined in the table below:

InvestmentImpact (Assumption)
Informational campaign on the dangers of smoking in all schools and free copies of the book “The Easy Way to Stop Smoking” for all smokers who request it1% reduction in smoking-related deaths: 830 lives saved per year
Doubling free mammograms (every year instead of every two years)10% reduction in breast cancer deaths annually: 1,200 lives saved per year
Installing speed enforcement systems on all highways and tripling alcohol-related checks5% reduction in road deaths: 170 lives saved per year

How should we decide how to allocate the €120 million? Is it wise to invest it in counterterrorism (which has caused 488 deaths across Europe in the past 15 years) rather than in breast cancer prevention, which could save 1,200 women per year in Italy alone?

It’s legitimate to think that the Paris attacks did not just cause 136 deaths but also created a sense of insecurity. But how do we determine the value of a life lost to terrorism compared to one lost in a road accident?

How can we allocate our €120 million wisely, rather than being emotionally swayed by recent events?

What do you think? Share your thoughts in the comments!

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