An Associated Press article captured the attention of readers with the headline “Night lights bad for kids?” The article was based on a 1999 study at the University of Pennsylvania and Children’s Hospital of Philadelphia, in which parents were surveyed about the lighting conditions under which their children slept between birth and age 2 (lamp, night-light, or no light) and whether or not their children developed nearsightedness (myopia). The purpose of the study was to explore the effect of a young child’s nighttime exposure to light on later nearsightedness.

To answer the questions below, we provide you with both SAS and SPSS output, but we encourage you to try and generate this output yourself in your chosen statistical software.


  • Create Two-Way tables: ANALYZE > DESCRIPTIVE STATISTICS > CROSSTABS, complete the wizard (4 times) to obtain
    • Two-way table with the count (frequency) and percent (out of total)
    • Two-way table with the count (frequency) and row percents
    • Two-way table with the count (frequency) and column percents
    • Two-way table with the count (frequency), row and column percents


  • Create Two-Way tables: Use PROC FREQ and the tables statement to create a two-way table with light and nearsightedness

Data: nightlight.xls or nightlight.csv

Learn By Doing
Question prompt


A Choice 1
B Choice 2
C Choice 3
D Choice D
E Choice E
F Choice F
G Choice G
H Choice H
Our Answer Comments.