Percentage increase since 2012 in the number of Americans who play lacrosse : 35

Rank of lacrosse among sports with the highest rates of concussions in adolescents : 2

Centimeters at which the Korean Basketball League caps the height of foreign players : 200

Portion of players in the 2017–18 Golden State Warriors
roster who would be disqualified : 13/16

Rank of North Korea’s nuclear program among South Koreans’
greatest sources of anxiety : 6

Of air pollution : 1

Estimated average age, in years, of a car in Poland : 17

Number of the European Union’s fifty most polluted cities that are in Poland : 33

Estimated total number of trees that US urban areas lose each year : 28,000,000

Portion of adult New York City apartment dwellers who smelled cigarette smoke from the street or another unit in 2016 : 1/2

Estimated additional rent paid by New Yorkers in 2016
because of Airbnb : $616,743,319

Estimated percentage of homeless people in New York City who are unsheltered : 6

Of homeless people in Los Angeles : 75

Percentage of urban Americans who say they know most or all of their neighbors : 24

Of rural Americans : 40

Percentage of US couples with an annual income of less than $75,000 who are “very happy” with their sex life : 46

Of couples with an annual income of more than $200,000 : 65

Percentage of Irish aged 14 to 24 who consider internet articles useful for information about healthy sexual relationships : 91

Who consider their parents useful : 51

Portion of Irish aged 18 to 24 who believe one can contract HIV from sitting on a toilet seat : 1/5

Percentage of Alabamians who oppose gay marriage : 51

Number of other states in which a majority of residents oppose it : 0

Percentage of LGBTQ teenagers who say they can “definitely”
be themselves at home : 24

At school : 27

Percentage of US public-school teachers who spend their own money on school supplies : 94

Average amount a teacher spends each school year : $479

Percentage change since 2008 in the average US public-school teacher’s salary : –4

Percentage change from 2010 to 2017 in the number of foreign teachers arriving annually to work in US public schools : +140

Percentage of white evangelical Americans who think the United States has a responsibility to accept refugees : 25

Of religiously unaffiliated Americans : 65

Portion of US refugee resettlement offices that have closed since Donald Trump’s inauguration : 1/7

Estimated average number of guns legally purchased in Mexico every day : 33

Of guns smuggled into Mexico from the United States : 246

Percentage change this year in the number of police and public safety officers employed by US colleges and universities : +30

Percentage of US college freshmen in 2010 who described themselves as having a psychological disorder : 4

In 2016 : 11

Percentage of US dog owners who say their pets sometimes have
anxiety or stress issues : 85

Who say they gave their pets medication to manage anxiety, calm them down, or control mood : 8

Minimum number of scientific papers published on nomophobia, the fear of not having access to cellular service : 55

“Harper’s Index” is a registered trademark.

August Index Sources

1 Sports and Fitness Industry Association (Silver Spring, Md.)
2 Zachary Kerr, University of North Carolina at Chapel Hill
3 Korean Basketball League (Seoul)
4 Golden State Warriors (Oakland, Calif.)
5, 6 Korea Institute for Health and Social Affairs (Sejong City)
7 European Automobile Manufacturers’ Association (Brussels)
8 World Health Organization (Bonn, Germany)
9 US Forest Service (Syracuse, N.Y.)
10 NYC Department of Health and Mental Hygiene
11 Office of the New York City Comptroller
12 NYC Department of Homeless Services
13 Los Angeles Homeless Services Authority
14, 15 Pew Research Center (Washington)
16, 17 eHarmony (San Francisco)
18,19 Youth Work Ireland (Dublin)
20 HIV Ireland (Dublin)
21, 22 Public Religion Research Institute (Washington)
23, 24 Human Rights Campaign (Washington) 
25, 26 National Center for Education Statistics (Washington)
27 National Education Association (Washington)
28 US Department of State
29, 30 Pew Research Center
31 US Department of State
32 Mexican Commission for the Defense and Promotion of Human Rights (Mexico City)
33 Topher McDougal, University of San Diego
34 College and University Professional Association for Human Resources (Knoxville, Tenn.)
35, 36 Higher Education Research Institute (Los Angeles)
37, 38 Packaged Facts (Rockville, Md.)
39 National Library of Medicine (Bethesda, Md.).