Here are a couple:
- Parents: https://pmc.ncbi.nlm.nih.gov/articles/PMC3353148/pdf/nihms37...
- People who have DS: https://pmc.ncbi.nlm.nih.gov/articles/PMC3740159/pdf/nihms37...
- Siblings of people with DS: https://doi.org/10.1002/ajmg.c.30101
- Parents: https://pmc.ncbi.nlm.nih.gov/articles/PMC3353148/pdf/nihms37...
- People who have DS: https://pmc.ncbi.nlm.nih.gov/articles/PMC3740159/pdf/nihms37...
- Siblings of people with DS: https://doi.org/10.1002/ajmg.c.30101
Definitely no sampling bias here... And given that the vast majority of people who do prenatal screening decide not to have a child with Down Syndrome, I don't think the people who choose to have a Down Syndrome child are really representative of prospective parents as a whole.
The revealed preference is clear, particularly in places like Iceland where prenatal screening is ubiquitous. They have effectively eradicated Down Syndrome going forward.
Why on EARTH would the opinions of people who were so scared of the experience that they never tried it at all even for a minute be relevant to that perspective?
Also, people who have had negative experiences raising a child with Down Syndrome are presumably far less likely to be involved with non-profit organizations related to Down Syndrome.