3 ways to spot a bad statistic
“ I want to give you guys three questions that will help you be able to spot some bad statistics. So, question number one is: Can you see uncertainty? One of things that has really changed people’s relationship with numbers, and even their trust in the media, has been the use of political polls. I personally have many issues with political polls because I think the role of journalists is actually to report the facts and not attempt to predict them, especially when those predictions can actually damage democracy by signaling to people: do not bother to vote for that guy, he doesn’t have a chance. Let us set that aside for now and talk about the accuracy of this endeavor.
Based on national elections in the UK, Italy, Israel and of course, the most recent US presidential election, using polls to predict electoral outcomes is about as accurate as using the moon to predict hospital admissions. No, seriously, I used actual data from an academic study to draw this. There are a lot of reasons why polling has become so inaccurate. Our societies have become really diverse, which makes it difficult for pollsters to get a really nice representative sample of the population for their polls. People are really reluctant to answer their phones to pollsters, and also, shockingly enough, people might lie. But you wouldn’t necessarily know that to look at the media. For one thing, the probability of a Hillary Clinton win was communicated with decimal places. We don’t use decimal places to describe the temperature. How on earth can predicting the behavior of 230 million voters in this country be that precise? And then there were those sleek charts. See, a lot of data visualizations will overstate certainty, and it works — these charts can numb our brains to criticism. When you hear a statistic, you might feel skeptical. As soon as it’s buried in a chart, it feels like some kind of objective science, and it’s not.
So I was trying to find ways to better communicate this to people, to show people the uncertainty in our numbers. What I did was I started taking real data sets, and turning them into hand-drawn visualizations, so that people can see how imprecise the data is; so people can see that a human did this, a human found the data and visualized it. For example, instead of finding out the probability of getting the flu in any given month, you can see the rough distribution of flu season. This is —
a bad shot to show in February. But it’s also more responsible data visualization, because if you were to show the exact probabilities, maybe that would encourage people to get their flu jabs at the wrong time.
The point of these shaky lines is so that people remember these imprecisions, but also so they don’t necessarily walk away with a specific number, but they can remember important facts. Facts like injustice and inequality leave a huge mark on our lives. Facts like Black Americans and Native Americans have shorter life expectancies than those of other races, and that isn’t changing anytime soon. Facts like prisoners in the US can be kept in solitary confinement cells that are smaller than the size of an average parking space.
The point of these visualizations is also to remind people of some really important statistical concepts, concepts like averages. So let’s say you hear a claim like, “The average swimming pool in the US contains 6.23 fecal accidents.” That doesn’t mean every single swimming pool in the country contains exactly 6.23 turds. So in order to show that, I went back to the original data, which comes from the CDC, who surveyed 47 swimming facilities. And I just spent one evening redistributing poop. So you can kind of see how misleading averages can be. OK, so the second question that you guys should be asking yourselves to spot bad numbers is: Can I see myself in the data? This question is also about averages in a way, because part of the reason why people are so frustrated with these national statistics, is they don’t really tell the story of who’s winning and who’s losing from national policy. It’s easy to understand why people are frustrated with global averages when they don’t match up with their personal experiences. I wanted to show people the way data relates to their everyday lives. I started this advice column called “Dear Mona,” where people would write to me with questions and concerns and I’d try to answer them with data. People asked me anything. questions like, “Is it normal to sleep in a separate bed to my wife?” “Do people regret their tattoos?” “What does it mean to die of natural causes?”
All of these questions are great, because they make you think about ways to find and communicate these numbers. If someone asks you, “How much pee is a lot of pee?” which is a question that I got asked, you really want to make sure that the visualization makes sense to as many people as possible. These numbers aren’t unavailable. Sometimes they’re just buried in the appendix of an academic study. And they’re certainly not inscrutable; if you really wanted to test these numbers on urination volume, you could grab a bottle and try it for yourself.
The point of this isn’t necessarily that every single data set has to relate specifically to you. I’m interested in how many women were issued fines in France for wearing the face veil, or the niqab, even if I don’t live in France or wear the face veil. The point of asking where you fit in is to get as much context as possible. So it’s about zooming out from one data point, like the unemployment rate is five percent, and seeing how it changes over time, or seeing how it changes by educational status — this is why your parents always wanted you to go to college — or seeing how it varies by gender. Nowadays, male unemployment rate is higher than the female unemployment rate. Up until the early ’80s, it was the other way around. This is a story of one of the biggest changes that’s happened in American society, and it’s all there in that chart, once you look beyond the averages. The axes are everything; once you change the scale, you can change the story.
OK, so the third and final question that I want you guys to think about when you’re looking at statistics is: How was the data collected? So far, I’ve only talked about the way data is communicated, but the way it’s collected matters just as much. I know this is tough, because methodologies can be opaque and actually kind of boring, but there are some simple steps you can take to check this.
I’ll use one last example here. One poll found that 41 percent of Muslims in this country support jihad, which is obviously pretty scary, and it was reported everywhere in 2015. When I want to check a number like that, I’ll start off by finding the original questionnaire. It turns out that journalists who reported on that statistic ignored a question lower down on the survey that asked respondents how they defined “jihad.” And most of them defined it as, “Muslims’ personal, peaceful struggle to be more religious.” Only 16 percent defined it as, “violent holy war against unbelievers.” This is the really important point: based on those numbers, it’s totally possible that no one in the survey who defined it as violent holy war also said they support it. Those two groups might not overlap at all.
It’s also worth asking how the survey was carried out. This was something called an opt-in poll, which means anyone could have found it on the internet and completed it. There’s no way of knowing if those people even identified as Muslim. And finally, there were 600 respondents in that poll. There are roughly three million Muslims in this country, according to Pew Research Center. That means the poll spoke to roughly one in every 5,000 Muslims in this country.
This is one of the reasons why government statistics are often better than private statistics. A poll might speak to a couple hundred people, maybe a thousand, or if you’re L’Oreal, trying to sell skin care products in 2005, then you spoke to 48 women to claim that they work.
Private companies don’t have a huge interest in getting the numbers right, they just need the right numbers. Government statisticians aren’t like that. In theory, at least, they’re totally impartial, not least because most of them do their jobs regardless of who’s in power. They’re civil servants. And to do their jobs properly, they don’t just speak to a couple hundred people. Those unemployment numbers I keep on referencing come from the Bureau of Labor Statistics, and to make their estimates, they speak to over 140,000 businesses in this country.
I get it, it’s frustrating. If you want to test a statistic that comes from a private company, you can buy the face cream for you and a bunch of friends, test it out, if it doesn’t work, you can say the numbers were wrong. But how do you question government statistics? You just keep checking everything. Find out how they collected the numbers. Find out if you’re seeing everything on the chart you need to see. But don’t give up on the numbers altogether, because if you do, we’ll be making public policy decisions in the dark, using nothing but private interests to guide us.”
Mona Chalabi – A British data journalist and writer of Iraqi descent