Movements of small blue periwinkles

Direction and distance moved by 31 small blue periwinkles (Nodilittorina unifasciata) after they were transplanted downshore from the height at which they normally live. This is Fisher's (1993) data set B.20 – the worked example threaded through his Section 6.4 on circular-response regression (Examples 6.3 and 6.9–6.11). It is bundled here with the radian and mean-centred columns the circ_lm fits use, so no manual conversion is needed.

Usage

periwinkles

Format

A data frame with 31 rows and 4 columns:

theta.deg

Direction moved, in degrees (compass bearing; the sea lay at roughly \(275^\circ\)).

x

Distance moved, in metres.

theta.rad

theta.deg in radians (theta.deg * pi / 180).

xc

x centred at its mean.

Source

Fisher, N. I. (1993) Statistical Analysis of Circular Data. Cambridge University Press, Appendix B.20 (pp. 252–253).

Examples

## Fisher-Lee mixed model: mean and log-kappa both linear in distance (Ex. 6.11)
circ_lm(list(theta.rad ~ x, ~ x), data = periwinkles, type = "cl")