artificial intelligence Monitoring National Center for Biotechnology Information NCBI NLM MEDLINE humans pubmed abstract nih national institutes of health national library of medicine models statistical reproducibility of results research support non-u.s. gov't algorithms enrique garcia-ceja sensitivity and specificity time factors pmid:25436652 pmc4299024 doi:10.3390/s141222500 ramon f brena leonardo garrido accelerometry / methods* actigraphy / methods* computer simulation data interpretation longitudinal studies markov chains ambulatory / methods* motor activity / physiology* pattern recognition automated / methods*