Which design is appropriate for comparing slug abundance before and after a rain event?

• A. Paired counts in matched plots
• B. Unpaired counts in random plots
• C. A single plot with no replication
• D. A cross-sectional survey

Answer: (A)

Comparing slug abundance before and after an event is best done with measurements taken on the same plots at both times. Paired counts in matched plots accomplish this by measuring slug numbers in the same locations before and after the rain, so differences between plots don’t obscure the change caused by the event. This approach increases statistical power because the analysis focuses on within-plot change, using each plot as its own control. If you used unpaired counts in random plots, you’d be mixing results from different plots at the two times, and variation between plots could mask the rain’s effect. A single plot with no replication provides no sense of natural variation and can’t support a before-after comparison. A cross-sectional survey measures at one time point (or across many plots without a before measurement) and can’t capture change over time. Therefore, paired counts in matched plots is the appropriate design.