brokenstick() ignores the last observation

[stefvanbuuren]

The default setting in for the Boundary.knots argument of brokenstick() (2.5.0) ignores the data in the last, rightmost observation in a specific situation.

The default Boundary.knots are set as follows (from the JSS paper):

These conditions require that Boundary.knots span at least the range of the data. This requirement is easy to achieve by setting Boundary.knots = range(data$age), which is done by default. Also, we need to ensure that the range of knots is not outside Boundary.knots. We may achieve that by setting Boundary.knots to include at least range(knots).

Somewhat unexpectedly, the current version ignores the data from the last knot if these show no age variation (i.e. if all observations are made at the same time). This may occur when the data have been pre-arranged or rounded into waves.

A quick solution is to manually set the right boundary knot slightly higher than the last knot value. For example, if the knots = c(0, ..., 10) then set boundary = c(0, 11).

Ideally, the procedure should test for this case, and adapt the default.

[stefvanbuuren]

Related #4