In early studies, the data gathered by citizen scientists were often too vague to be used, says Matthew Stevens, monitoring coordinator for the Appalachian Trail Conservancy (ATC) in Lyme, New Hampshire. “The data were not precise enough,” Stevens recalls. The problem was that the data generated by volunteers sometimes represented a range rather than specific numbers, which made it difficult to detect changes or to support conclusions. Now, citizen scientists are trained to read instruments and provide actual numbers. Be cautious, however, Shirk advises: study leaders can err on the other side by asking volunteers to collect data that are too complex or detailed.