optional MOE input for approximate_median

[sastoudt]

We may want an optional moe input field for approximate_median to handle the case when the n values are estimates themselves (e.g. outputs of approximate_sum). The approximate_median would then need a simulation aspect to account for the n values' uncertainty.

[sastoudt]

Proof of concept here.

[palewire]

This would be a step beyond what the Census Bureau does or recommends. It would be a great add, but we can also live without it

[sastoudt]

dealt with in #20