Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Tell me the sum of Year for outcome of runner-up for world darts championship

### Inputs:
table_name: table, columns: ['Outcome', 'Year', 'Championship', 'Opponent in the final', 'Score (l) = score in legs, (s) = score in sets.']

### Response:
SELECT SUM Year FROM table WHERE Outcome = runner-up AND Championship = world darts championship