Hello,

We have a 3*3*2*2*2*2*3*3= 3^4*2^4 (i.e. Total eight factors: four factors with two levels each, and four factors with three levels each) design. One of our factors is Age, which has three levels (Young, Young-Old, and Old-Old). From previous literature about online surveys, we can reasonably foresee that there will be few Young-Old (aged 61-74) and very few Old-Old(aged 85 and older) subjects in our sample. Thus, to avoid sample bias, we plan to use demographic filters of online survey platforms to select participants. Would you please give us some advice about how to calculate the minimum number of Young-Old and Old-Old subjects that we need?

More Information About Our Design: There is a total of 36 cells. According to the power analysis, the total sample size needed is 1364. （One exploratory calculation is that because there are three levels of Age, we will need 1364/3= 455 in each level, i.e. 455 Young, 455 Young-Old, and 455 Old-Old subjects. It doesn't seem correct.）

Thank you for your time and help in advance!