Probably Overthinking It

In 2019 I presented a talk at SciPy where I showed that support for gun control has been declining in the U.S. since about 1999. And, contrary to what many people believe, it is lowest among millennials and Gen Z.

Those results were based on data from the General Social Survey up to 2018. Now that the data from 2021 is available, I’ve run the same analysis and I can report:

• Support for gun control has continued to decline, and
• Among young adults it has reached a new low.

The following figure shows the fraction of GSS respondents who said that they would favor “a law which would require a person to obtain a police permit before he or she could buy a gun.”

Support for this form of gun control increased between 1972 and 1999, and has been decreasing ever since.

The following figure shows the results from the same question plotted over year of birth.

People born between 1890 and 1970 supported gun control at about the same level. More recent generations — including millennials and Gen Z — are substantially less likely to support gun control.

Some time in the next 10-15 years, the most common religion in the United States will be “none”.

In this figure, the solid lines show estimated proportions of each religious affiliation from 1972 to 2021. Since the early 1990s, the proportion of Protestants has been declining and the proportion of people with no religious affiliation has been increasing. Catholicism has declined slightly and other religions have increased slightly.

Some of the data from 2021 is out of line with long-term trends. The pandemic affected data collection in several ways, so we should not make too much of these results for now.

The shaded areas show results from a model I used to fit past data and forecast future changes. The model predicts that “Nones” will overtake Protestants in the 2030s. The primary cause of these changes is generational replacement: as older people die, they are replaced by young people who are less likely to be religious. The following figure shows the proportion of each religious tradition as a function of year of birth:

Among people born around 1900, nearly all were Protestant or Catholic; few belonged to another religion or none. Among people born around 2000, the plurality have no religious affiliation; Protestants and Catholics are statistically tied for second.

In general, forecasting social phenomena is hard because things change. However, generational replacement is relatively predictable. To see how predictable, let’s see what would have happened if we used the same method to generate predictions 15 years ago:

Predictions made in 2006 (using only the data in the shaded area) would have been pretty good. We would have underestimated the growth of the Nones, but the predictions for the other groups would have been accurate. So we have reason to think 15-year predictions based on current data are reliable.

If you want details, the model is multinomial logistic regression using two features: year of birth and year of survey. It is based on the assumption that (1) the distribution of ages will not change substantially over the next 15 years, and (2) most people don’t change religious affiliation as adults, or if they do, the resulting net flow between affiliations is small.

I have news. I finished the last two chapters of Probably Overthinking It last week and sent a complete draft of the book off for technical review. Yay!

In the last chapter, I used some methodology I thought was worth reporting, but too technical for the book, which is intended for an intelligent general audience. So I’ve started a public site for the book, where I will post technical details from each chapter and maybe some of the material that I decided to cut.

The last chapter is about changes in political beliefs over the last 50 years, particularly along the axis of liberal and conservative views. I found 15 questions in the General Social Survey (GSS) where liberals and conservatives give different answers by the widest margin. The following figure shows the topics, which will come as no surprise, and the differences between the groups.

Based on the answers to these questions, I estimate a score for each respondent that quantifies how conservative their beliefs are. By this measure, people have been getting more liberal, pretty consistently, for the last 50 years:

And it’s not just liberals becoming more liberal. People who consider themselves conservative are more liberal than they used to be, too.

That gray line is at 6.8 conservative responses, which was the expected level in 1974 among people who called themselves liberal.

Now, suppose you take a time machine back to 1974, find an average liberal, and bring them to the turn of the millennium. Based on their survey responses, they would be indistinguishable from the average moderate in 2000.

And if you bring them to 2021, their quaint 1970s liberalism would be almost as far to the right as the average conservative.

If you are curious about the methodology, here’s the article explaining where these results came from.

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