If I am invited do I have to take part?

The study is designed to cause minimal inconvenience to you. It is up to you to decide whether or not to take part. If you decide to take part, you are free to withdraw consent at any time without giving a reason. This would not affect the standard of medical care you receive. If you decide that you no longer wish to continue with the study, we would like to retain any data already obtained about you, unless you request otherwise.