The PDF file you selected should load here if your Web browser has a PDF reader plug-in installed (for example, a recent version of Adobe Acrobat Reader).

If you would like more information about how to print, save, and work with PDFs, Highwire Press provides a helpful Frequently Asked Questions about PDFs.

Alternatively, you can download the PDF file directly to your computer, from where it can be opened using a PDF reader. To download the PDF, click the Download link above.

Fullscreen Fullscreen Off

Copyright Kay Downey and Yin Zhang


Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Article Views (By Year/Month)

2026
January: 10
2025
January: 42
February: 55
March: 50
April: 41
May: 26
June: 44
July: 35
August: 53
September: 64
October: 69
November: 99
December: 78
2024
January: 24
February: 23
March: 21
April: 25
May: 32
June: 29
July: 23
August: 17
September: 22
October: 9
November: 16
December: 12
2023
January: 42
February: 31
March: 41
April: 19
May: 26
June: 26
July: 17
August: 12
September: 24
October: 19
November: 16
December: 19
2022
January: 44
February: 38
March: 152
April: 159
May: 56
June: 14
July: 26
August: 27
September: 20
October: 26
November: 22
December: 20
2021
January: 40
February: 48
March: 64
April: 39
May: 44
June: 42
July: 33
August: 29
September: 21
October: 41
November: 24
December: 45
2020
January: 595
February: 186
March: 81
April: 64
May: 65
June: 69
July: 62
August: 41
September: 53
October: 54
November: 60
December: 32