BCal help system: The Tutorial

Step A17: Floating parameter elicitation

The final part of the elicitation process is to define any floating parameters. Earlier on, we specified there to be one floating parameter. This page allows us to define this floating parameter. The floating parameter is to represent the date associated with the arrival of the Polynesians in Hawaii. We have both relative and absolute a priori chronological information for this event.

The page is split into three parts. The first part asks for a label for this parameter. Again, adopting the convention in the literature, we usually label all floating parameters as "phi" followed by a number (or word).

The next part allows us to define the absolute a priori chronological information. We define this in the same way as we do for group boundary parameters. As stated in the introduction, the archaeologists' best estimate for the arrival date of the Polynesians can be represented by a normal distribution with a mean of 1350 cal BP (which is equal to 600 AD) and a standard deviation of 100 calendar years. BCal allows us to specify this directly.

The last part of the page allows us to define the relative a priori chronological information. We are able to specify this information by identifying which parameters are known to be earlier and later than this floating parameter. The Polynesians must have arrived before the creation of the pond (which is represented by beta 1), i.e. we know that beta 1 is later than this floating parameter. We can express this by selecting beta 1 in the list of later parameters.

Note 1: When we defined the parameters that are earlier and later than this parameter, we only set beta 1 to be later. It is also true that alpha 2, theta 2, theta 3, theta 4, theta 5 and beta 2 are later. These parameters all belong to Layer II. Since we specified that Layer II abuts and is later than Layer III, it follows that all of these parameters are later than (or equal to, in the case of alpha 2) beta 1. If these parameters are later than (or equal to) beta 1, and beta 1 is later than the floating parameter, these parameters must also be later than the floating parameter. BCal automatically deduces relationships like this.

Note 2: You may notice a question mark (?) in the lists of parameters. This represents the floating parameter which will not be assigned a name until the current page is submitted.