Cut-points expressed in gravitational units (this vignette)

This vignette focuses on cut-points for metrics that attempt to quantify average acceleration per epoch in gravitational units. The strength of these metrics is that their values are not affected by sampling rate and epoch length improving comparability across studies.

Cut-points NOT expressed in gravitational units (not in this vignette)

However, GGIR also facilitates some metrics whose values are not expressed in gravitational units that were historically used. For example, the metric as described by Neishabouri (see GGIR argument do.neishabouricounts) which reflects the indicator of accumulated body movement over time, referred to as counts, calculated by the ActiLife software from the ActiGraph accelerometer brand. Cut-points for counts corresponding to the ActiGraph brand have been recurrently proposed in the literature, for example, see this systematic review with a stratification by age group. Note that cut-points for ActiGraph counts proposed before the introduction of multiday raw data collection are most likely hardware-based calculations which may not perfectly align with ActiGraph software-based (Actilife) calculations of counts that Neishabouri described. As a result, older cut-points may need to be used with caution.

The cut-points you find in the literature for ActiGraph counts cannot be applied to Neishabouri counts directly because both are epoch length specific. The cut-points from the literature need to be corrected by a conversion factor. The conversion factor is calculated as the epoch length in the new study (e.g. 5 seconds) divided by the epoch length in the original study (e.g. 60 seconds). Note that no correction for differences in sampling rate is needed because Neishabouri counts already account for this via down-sampling.

If we would want to use cut-point “100 counts per minute” from the literature on 5 second epoch data, the GGIR function call would look like this:

GGIR([...],
     mode = 1:5,
     windowsizes = c(5, 900, 3600),
     do.neishabouricounts = TRUE,
     acc.metric = "NeishabouriCount_y",
     threshold.in = 100 * (5/60),
     [...])

Cut-points for preschoolers

*These publications used acceleration metrics that sum their values per epoch rather than average them per epoch like GGIR does. So, to use their cut-point in GGIR, we provide a scaled version of the cut-points presented in the paper as: (CutPointFromPaper_in_gsecs/85.7) * 1000. Note that sample frequency of 87.5 as reported in the publication was incorrect and based on correspondence with authors we replaced this by 85.7.

Cut-points for children/adolescents

*These publications used acceleration metrics that sum their values per epoch rather than average them per epoch like GGIR does. So, to use their cut-point in GGIR, we provide a scaled version of the cut-points presented in the paper as: (CutPointFromPaper_in_gmins/(sampleRateFromPaper * EpochLengthInSecondsPaper)) * 1000 ** This publication used acceleration metrics that expressed their cut-points in g units. So, to use their cut-point in GGIR, we provide a cut-point multiplied by 1000.

Cut-points for adults

*These publications used acceleration metrics that sum their values per epoch rather than average them per epoch like GGIR does. So, to use their cut-point in GGIR, we provide a scaled version of the cut-points presented in the paper as: (CutPointFromPaper_in_gmins/(sampleRateFromPaper * EpochLengthInSecondsPaper)) * 1000 ^† In this publication, there are cut-point based on data sampled at 30 Hz and 100 Hz. When scaling the cut-points as specified in (*), the resulting thresholds are virtually the same (the ones presented in this table).

Cut-points for older adults

*Cut-points derived from applying the Youden index on ROC curves.
** Cut-points derived from increasing Sensitivity over Specificity for light and vice versa for moderate on ROC curves (see paper for more details).
^† These publications used acceleration metrics that sum their values per epoch rather than average them per epoch like GGIR does. So, to use their cut-point in GGIR, we provide a scaled version of the cut-points presented in the paper as: (CutPointFromPaper_in_gmins/(sampleRateFromPaper * EpochLengthInSecondsPaper)) * 1000 ^‡ More cut-points excluding data on aided walking and washing up activities can be found in the publication.