abstract type AbstractEstimator{State} end


struct ImportanceEstimator{S, P <: Real} <: AbstractEstimator{S}
    states::Vector{S}
    logprobs::Vector{Vector{P}}
    rejections::Vector{Int}
end

#estimate(q::Q) = 

levels = length.(logprobs)
for l = 1:L
s = states[(levels .== l)]
mean(s)
end