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On the use of approximate entropy and sample entropy with centre of pressure time-series
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Montesinos-Silva, Luis, Castaldo, Rossana and Pecchia, Leandro (2018) On the use of approximate entropy and sample entropy with centre of pressure time-series. Journal of NeuroEngineering and Rehabilitation, 15 (1). 116. doi:10.1186/s12984-018-0465-9
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Official URL: http://dx.doi.org/10.1186/s12984-018-0465-9
Abstract
Background
Approximate entropy (ApEn) and sample entropy (SampEn) have been previously used to quantify the regularity in centre of pressure (COP) time-series in different experimental groups and/or conditions. ApEn and SampEn are very sensitive to their input parameters: m (subseries length), r (tolerance) and N (data length). Yet, the effects of changing those parameters have been scarcely investigated in the analysis of COP time-series. This study aimed to investigate the effects of changing parameters m, r and N on ApEn and SampEn values in COP time-series, as well as the ability of these entropy measures to discriminate between groups.
Methods
A public dataset of COP time-series was used. ApEn and SampEn were calculated for m = {2, 3, 4, 5}, r = {0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5} and N = {600, 1200} (30 and 60 s, respectively). Subjects were stratified in young adults (age < 60, n = 85), and older adults (age ≥ 60) with (n = 18) and without (n = 56) falls in the last year. The effects of changing parameters m, r and N on ApEn and SampEn were investigated with a three-way ANOVA. The ability of ApEn and SampEn to discriminate between groups was investigated with a mixed ANOVA (within-subject factors: m, r and N; between-subject factor: group). Specific combinations of m, r and N producing significant differences between groups were identified using the Tukey’s honest significant difference procedure.
Results
A significant three-way interaction between m, r and N confirmed the sensitivity of ApEn and SampEn to the input parameters. SampEn showed a higher consistency and ability to discriminate between groups than ApEn. Significant differences between groups were mostly observed in longer (N = 1200) COP time-series in the anterior-posterior direction. Those differences were observed for specific combinations of m and r, highlighting the importance of an adequate selection of input parameters.
Conclusions
Future studies should favour SampEn over ApEn and longer time-series (≥ 60 s) over shorter ones (e.g. 30 s). The use of parameter combinations such as SampEn (m = {4, 5}, r = {0.25, 0.3, 0.35}) is recommended.
| Item Type: | Journal Article | |||||||||
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| Subjects: | Q Science > QP Physiology | |||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Engineering > Engineering | |||||||||
| Library of Congress Subject Headings (LCSH): | Equilibrium (Physiology) -- Mathematical models, Time-series analysis, Entropy | |||||||||
| Journal or Publication Title: | Journal of NeuroEngineering and Rehabilitation | |||||||||
| Publisher: | BioMed Central Ltd. | |||||||||
| ISSN: | 1743-0003 | |||||||||
| Official Date: | 12 December 2018 | |||||||||
| Dates: |
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| Volume: | 15 | |||||||||
| Number: | 1 | |||||||||
| Article Number: | 116 | |||||||||
| DOI: | 10.1186/s12984-018-0465-9 | |||||||||
| Status: | Peer Reviewed | |||||||||
| Publication Status: | Published | |||||||||
| Access rights to Published version: | Open Access | |||||||||
| RIOXX Funder/Project Grant: |
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