than adopting children do so because they value a biological connection to their children. At the same time, because the donation is anonymous they deny their children the opportunity to connect with half of their biological tree. This is can be viewed as hypocritical of the parents, and is an argument against anonymity for donors. Among donors and potential donors Among donors, a systematic review of 29 studies from nine countries concluded that 20–50% of donors would still be willing to donate even if anonymity could not be guaranteed. Between 40 and 97% of donors agree to release non-identifying information such as physical characteristics and level of education. The proportion of actual donors wishing for contact with their offspring varies between 10 and 88%. Most donors are not open to contact with offspring, although more open attitudes are observed among single and homosexual donors. About half of donors feel that degree of involvement should be decided by the intended parents. Some of the donors prefer contact with offspring in a non-visible way, such as where the child can ask questions but the donor will not reveal his identity. One study recruited donors through the Donor Sibling Registry who wanted contact with offspring or who had already made contact with offspring. It resulted that none of the donors said that there was "no relationship", a third of donors felt it was a special relationship, almost like a very good friend, and a quarter felt it was merely a genetic bond and nothing more. Fifteen percent of actual donors considered offspring to be "their own children". On the whole, donors feel that the first step towards contact should come from offspring rather than parents or the donor himself. Some even say that it is the moral responsibility of the donor not to seek contact with offspring. The same review indicated that up to 37% of donors reported changes in their attitude towards anonymity before and after donation, with one in four being prepared to be more open about themselves after the donation than before (as a "potential donor"). Among potential donors, 30–46% of potential donors would still be willing to donate even if anonymity could not be guaranteed. Still, more than 75% of these potential donors felt positive towards releasing non-identifying information to offspring, such as physical characteristics and level of education. Single or homosexual men are significantly more inclined to release