Urgent:
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1. convert to Hmisc weighted SD, quantile, table, etc. functions

Interesting:
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1. PCA by depth slice
2. user-defined slices for profile_compare()
3. objective selection of k
4. sensitivity analysis on profile_compare()
5. equal-area splines
6. check profile-level weighting scheme

Website:
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1. more examples
2. more figures