Learn By Doing – Causation
When we practiced exploring the relationship between two categorical variables, we looked at a study in which the type of light in young children’s rooms when they sleep was examined, along with their later nearsightedness, or myopia.
Here is the two-way table that summarizes the collected data:
The conditional percentages allow us to compare the distribution of later nearsightedness among children who were exposed to each of the three nighttime light levels:
The striking finding was that children who slept with lamps on were more than 5 times more likely to be nearsighted later in life (54.7% vs. 9.9%). Based upon this data alone, parents might discontinue using night-lights and lamps with young children.
This document is linked from Causation.