There's a gazillion twin studies out there. There are huge databases of twins to facilitate their creation. It's really not that difficult. They might be imperf

There's a gazillion twin studies out there. There are huge databases of twins to facilitate their creation. It's really not that difficult. They might be imperfect but I would not call them unreliable. We already know from earlier twin studies that genetics play a large role in literacy and numeracy.[0][1] So it's not like this is a shot in the dark, everyone already knows it's a confounder that must be taken into account. [0] https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7610.1987.tb00207.x https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7610.... [1] http://journals.sagepub.com/doi/abs/10.1177/0956797613486982 http://journals.sagepub.com/doi/abs/10.1177/0956797613486982