1 % of (the) GDP - with or without the article?

What is the correct form? I have consistently encountered both forms. Definite article: required, optional or wrong?


Both forms are used commonly; however, the pattern seems to be that if a proper name follows the term GDP, then the article the is attached to GDP

5% of the GDP of Australia

whereas if no proper name follows GDP, then the article is not attached.

5% of GDP is lost.