I'm conducting an online mental health survey. I only want adults aged 18 years and over to complete it. Is it appropriate to block under 18s by having a "forced response to age and a minimum of 18 years old"?
Yes, depending on what countries you are surveying you may well need parental approval to give the survey to under 18. Many researchers find it easier just to include adult aged 18 and over (unless of course the study is of children).