The occupation continuity index

The occupation continuity index measures the percentage of sites occupied during the preceding phase which continued to be occupied during the phase in question. Its complement is thus the percentage of sites occupied in the preceding phase which were abandoned in the current phase.

  
$I_{oc}=100\frac{S_{po}}{S_{pn}}$ 




where $I_{oc}$ = occupation continuity index 


		 		 $S_{po}$ = number of site occupied in previous phase still occupied in phase 


		 		 $S_{pn}$ = number of sites ocupied in previous phase no longer occupied in phase

Obviously, a high value means there was great occupation continuity from the preceding phase, whereas a low value indicates low continuity between phases.

Both the site founding index and the occupation continuity index were calculated using a simple Perl program, the source code to which is in Appendix E. When run, the program prompts the user for the name of an input file and two phases, earlier and later. The input file has two columns and is tab-delimited. The two columns are site number and phase (my phase coding conventions are defined in Appendix A). The program returns values for the site founding index and occupation continuity index, as well as some general information about the two phases selected. A sample run is shown below.

[/home/inti]> perl continuity.pl

Input file must be tab-delimited, and must contain 2 columns:

    1) Site, 2) Period  

Name or path of input file: site-phase.TAB 

    1: Early Formative 1

    2: Early Formative 2

    3: Middle Formative

    4: Late Formative 1

    5: Late Formative 2

    6: Tiwanaku

    7: Early Pacajes

    8: Pacajes-Inka

    9: Late Pacajes  

Calculate occupation continuity from:3

To: 4 

Working...  

Results:

    Total sites with a 2.0 occupation: 30

    Total sites with a 3.1 occupation: 54

    Sites with both 2.0 and 3.1 occupations: 22

    73 percent continuity between 2.0 and 3.1

    27 percent site abandonment rate

    59 percent new site founding rate  

Would you like another? n  

Okay. All done.

Press Enter to Exit

[/home/inti]>

The example is of the Middle Formative (2.0) and Late Formative 1 (3.1) phases (see Table 7.2). In this case, the results are a high rate of occupation continuity, and a moderate rate of site founding, indicating a stable and expanding settlement system.