Angela, taking the average IQ of the parents is known to be (by research) the best IQ estimate for their children? It seems logical, but I have never been able to find literature stating this fact. Very often, researchers speak about the correlation in IQ (between children and parents), but they do not explain how this correlation is calculated.
It's not quite as simple as that, i.e. a strict average.
I was being a bit flip. It will, however, be somewhere in that range. It's just so obvious that I can't understand the resistance to the idea that it's heritable and that one has to consider the IQ of both parents, especially in light of all the data that's been generated for decades.
There are many components to an IQ score. When you get recombination in the sex cells, there isn't a strict division.
I'm sure people are sick about hearing about my brother and me, but we're really a very good illustration of this. We're sort of mirror opposites of each other. On the SAT scores I got an 800 on the verbal and 720 on the math. He got 800 on the math and 720 on the verbal. Total IQ scores are in the same ballpark, but not exactly the same. He got more of certain skills and I got more of others. I think he is better functioning on the visual/spatial side of the equation because he got those alleles both from my mother's side (her father and a cousin were/are both engineers, the latter working on managing the water problem in Venice), and my father, wonderful at math, and very visually oriented (his dream had been to be an architect). I don't think I got those same alleles from my mother as my brother got. I got the verbal aptitude ones from her instead, with a brother and cousin who were writers and journalists, and from my father as well, along with some of his math skills. My brother's IQ is not only slightly higher than mine, but I think it's probably a bit higher than my father's and mother's as well. It's serendipity depending upon which specific alleles are inherited and how they influence one another.
Also, after awhile there's what they call regression toward the mean. For example, the children of two people with a genius level IQ will still have a high IQ, but perhaps not as high as the parents. It applies to things like musical ability too. The Bach family is an example. Generations of talented musicians, before and after him, but only one Johann Sebastian Bach, unfortunately.
You can also have rare cases where parents with high average IQ can produce a prodigy. Again, serendipity. Just the right combination of alleles from both lines, plus, perhaps, some de novo mutations.
Those are the subtleties.
The general takeaway is the same, however. The IQ of both parents is important, and the IQ of the child will more than likely be in the same ballpark as the parents sort of averaged. In most cases there isn't a big disparity in the IQ of the father versus the mother anyway, of course, because in this day and age assortative mating is particularly strong in the area of intellectual functioning. That wasn't always the case. Many marriages in the past, as I'm sure you know, were based on land and property, or an older man on his second or third wife just marrying someone on the basis of looks.
Fwiw, I looked up that sperm bank, and the Wiki article says that the media reports about the qualifications of the women "donees" were incorrect.
See:
https://en.wikipedia.org/wiki/Repository_for_Germinal_Choice