Tests whether the rest-activity rhythm differs between two groups. Fits each
subject's cosinor with the same engine as cosinor.analysis. An
Bingham et al. (1982) comparison is a 2-variate Hotelling's \(T^2\) on the
cosine and sine coefficients (testing equal amplitude and acrophase, accounting
for their correlation), with the MESOR compared by a separate pooled-variance
F-test. Auxiliary per-parameter two-sample (Welch) t-tests break the result
down for the MESOR, amplitude, and acrophase; the acrophase test is
circular-aware, unwrapping the per-subject acrophases about their common
circular mean.
Usage
cosinor.compare(
activity,
timestamps,
subject,
group,
period = 24,
level = 0.95,
min_valid_hours = 12
)Arguments
- activity
Numeric activity vector with all subjects stacked.
- timestamps
POSIXct timestamps, one per value.
- subject
Subject identifier, one per value.
- group
Group identifier (exactly two levels), one per value.
- period
Rhythm period in hours (default 24).
- level
Confidence level for the difference CIs (default 0.95).
- min_valid_hours
Minimum profile hours for a subject to be included.
Value
An object of class actiRhythm_cosinor_compare: a joint
list (the amplitude/acrophase Hotelling \(T^2\) with its F, degrees of
freedom and p-value, plus a separate MESOR F-test), a tests data frame
of auxiliary per-parameter Welch comparisons (each group's estimate, the
difference, the t statistic, p-value and CI), and the per-subject coefficients.
References
Bingham C, Arbogast B, Cornelissen Guillaume G, Lee JK, Halberg F (1982). “Inferential statistical methods for estimating and comparing cosinor parameters.” Chronobiologia, 9(4), 397–439.
Examples
set.seed(1); hrs <- 0:23
act <- ts <- subj <- grp <- NULL
for (g in c("A", "B")) for (i in 1:5) {
acro <- if (g == "A") 8 else 11
y <- 100 + 40 * cos(2 * pi * (hrs - acro) / 24) + rnorm(24, 0, 4)
act <- c(act, y); subj <- c(subj, rep(paste0(g, i), 24)); grp <- c(grp, rep(g, 24))
ts <- c(ts, as.POSIXct("2024-01-01", tz = "UTC") + hrs * 3600)
}
cosinor.compare(act, as.POSIXct(ts, tz = "UTC", origin = "1970-01-01"), subj, grp)
#> Cosinor Comparison Between Two Groups
#>
#> Groups: A (n=5) vs B (n=5)
#> Period: 24 h
#>
#> Amplitude/acrophase (Bingham T2): F(2,7) = 994.58 p = 2.55e-09
#> MESOR (Bingham F): F(1,8) = 1.70 p = 0.228
#>
#> mesor diff = +0.70 t(5.6) = 1.31 p = 0.243
#> amplitude diff = -0.22 t(7.8) = -0.34 p = 0.743
#> acrophase diff = -2.92 t(6.8) = -39.92 p = 2.77e-09