…First, research conducted with parents who used a donor to create their families shows that most do not tell their children the truth about the circumstances of their conception. This is true even in countries that have banned anonymity. Those who do not know that they are donor-conceived cannot be recruited to participate in research, which creates an insurmountable limitation to the study sample in any research on the life experiences of donor offspring.

Second, confidentiality issues make recruitment of this population exceptionally challenging and sample sizes are typically small (even the larger studies include less than 100 participants).

Third, typical recruitment strategies of research participants through support networks may lead to a significant selection bias, as it is likely that individuals are members of such networks precisely because they are suffering from identity issues or have specific interests.

Finally, because of these challenges, and because the majority of people with donor origins are still relatively young, no longitudinal studies (the gold standard in social science research) have been completed that would ideally follow individuals throughout life and record the impact of their unique status on various life stages and transitions.

Despite these challenges data have been consistently accumulating over the past decade from small studies conducted in different countries indicating that indeed donor-conceived individuals have a strong interest in having access to information about their donors…

They then write about several samples including that of the 485 donor offspring reported in My Daddy’s Name is Donor.