Dr Nguyen Is Studying How Amount of Sleep Influences Mood

Multiple Choice

Dr. Nguyen is studying how amount of sleep influences mood for kindergarteners. A sample of 100 children is selected. Fifty children are allowed to sleep for 11 hours each night. The other 50 children are awoken after 8 hours. After three nights, Dr. Nguyen records the mood for each child and compares the two groups of scores. In this example, how many levels are there for the independent variable?

A) 1
B) 2
C) 3
D) 100