Title: The threat of weighting biases in environmental deicison analysis

Authors: Raimo P. Hämäläinen and Susanna Alaja

Status: Systems Analysis Laboratory Research Reports E12, April 2003, Preliminary working draft of 10.5.2006

We investigate the existence of biases, in particular the so called splitting bias, in a real environmental decision analysis case. The splitting bias refers to a situation where presenting an attribute in more detail may increase the weight it receives. We test whether the splitting bias can be eliminated or reduced through instruction and training.

The test case used was the regulation of a lake-river system and the test group consisted of university students and local residents.

The splitting bias was not avoided even though the subjects were instructed about its threat. Most students avoided the bias. Nearly all of the local residents showed a systematic splitting bias so that the total weight of the attributes grew in proportion to the number of sub-attributes included.