user: Question: When +18.1 is the ± yes side 2008 percentage what is the percentage of against?
Columns: ['Constituency', 'Electorate', 's Spoilt vote', 'Total poll (%)', 'For (%)', 'Against (%)', '± Yes side 2008 (%)']
Types: ['text', 'real', 'real', 'text', 'text', 'text', 'text']
Sample row: ['Carlow–Kilkenny', 104387.0, 294.0, '60,254 (58.0)', '42,499 (70.5)', '17,755 (29.5)', '+20.5']
SQL:

assistant: SELECT "Against (%)" FROM "Table" WHERE "± Yes side 2008 (%)" = '+18.1';