Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_20683381_3 ( against___percentage_ VARCHAR, ±_yes_side_2008___percentage_ VARCHAR )

### Question ###
When +18.1 is the yes side 2008 percentage what is the percentage of against?

### Accurate SQL ###

SELECT against___percentage_ FROM table_20683381_3 WHERE ±_yes_side_2008___percentage_ = "+18.1"