map_nhanes_pa_quantiles
                        Map physical activity values to NHANES
                        population quantiles
nhanes_measure_data     NHANES PA data
nhanes_pa_age_category
                        Convert ages to NHANES physical activity CDF
                        age categories
nhanes_pa_quantile      Evaluate a single NHANES physical activity
                        quantile
precompute_nhanes_pa_cdfs
                        Precompute and cache NHANES PA CDFs
