Factorial Analysis of Cloud Seeding

In this activity, you will do a factorial analysis (Two-Way ANOVA) of data collected in a study to determine if there is a difference in rainfall due to cloud seeding during different seasons of the year.

Scientists are experimenting with ways to increase precipitation using new methods of cloud seeding. Cloud seeding is the deliberate treatment of specific clouds or cloud systems with the intent of altering the precipitation process within the clouds. Cloud seeding is utilized in order to: increase precipitation, improve visibility, and suppress hail. The majority of seeding is done to try to increase precipitation.

Cloud seeding causes super-cooled liquid water droplets to freeze. This process is achieved by  spraying  an ice-forming agent, such as silver iodide, into the clouds. If the conditions are favorable, droplets will form around the iodide particles and precipitation will begin. 

This data you will analyze comes from an experiment designed to determine if cloud seeding increased the precipitation in a region during the four seasons of the year.   In this activity you will determine if there is a significant difference in precipitation between the seeded and unseeded clouds during the seasons in which the data was collected.

Factor I
(Cloud Seeding)
SeededUnseeded
Winter8 rainfall points8 rainfall points
Factor IISpring8 rainfall points8 rainfall points
(Season)Summer8 rainfall points8 rainfall points
Autumn8 rainfall points8 rainfall points


Using the data set in Excel, perform a factorial Analysis (Two-Way ANOVA) to determine if there is a significant difference in precipitation produced between the seeded and unseeded clouds; between the different seasons; and if there was an interaction between cloud seeding and the seasons of the year. 

1.Is there a significant difference in the mean precipitation of seeded and unseeded clouds?
2. How do you know the answer to question 1?
3. Is there a significant difference in the mean precipitation between the seasons?
4. How do you know the answer to question 2?
5. Is there a significant interaction between the two factors (seasons and seeding of clouds)?
6. How do you know the answer to question 5?
7. What does the interaction term tell you about the relationship between the two factors?


Original work on this document was done  by Corey Barnes, Ashley Creasy, and Josh Middleton (Class of 2002)

Copyright © 2011 Central Virginia Governor's School for Science and Technology Lynchburg, VA