One of the most important tasks an archaeologist faces is discovering sites in the landscape. Unless a site is clearly visible, it is necessary to use various methods of subsurface testing, from simple test pits dug by hand to technologically advanced methods of remote sensing such as ground penetrating radar and magnetic surveying. However, because it is generally unfeasible to test an entire survey area, the archaeologist must decide on the sampling strategy that best suits his or her purposes.
Sampling strategies can be classified as either non-probabilistic or probabilistic. Non-probabilistic sampling is used when the archaeologist is most interested in already visible or suspected sites and does not need to sample elsewhere. Probabilistic sampling is used when it is necessary to have a representative sample of the sites in a region (the "sample universe"), but it is possible to sample only a small percentage of the whole. By employing statistical methods, probabilistic sampling attempts to increase the probability that generalizations derived from the sample will be correct.
The following aerial photographs of western Montana illustrate various sampling strategies. For this hypothetical archaeological survey, the illustrated region has been divided into 999 equal sampling units and in each example subsurface tests have been carried out on approximately 5% of the units. Note that the percent of the sample universe that is sampled depends upon the circumstances of the survey, and can be influenced by variables including: the nature of the environment, the types of sites, and the budget and timeframe of the project. For example, a different project with a larger budget could sample 20% of the units (200 squares) instead of approximately 5% (48 squares).
Exposed archaeological sites are coded yellow to illustrate how many have been found with each strategy. Examples of the results are illustrated by passing the cursor over each image. If you have a slow connection, please be patient while the images load. If using Netscape, you may have to hold the cursor over the image for a few moments while the image loads.
Of the many types of sampling strategies discussed here, all are useful in certain situations, but none is perfect. For example, a significant danger of using only probabilistic sampling techniques in field survey is that a major site may be overlooked, resulting in a skewed analysis of the archaeology of the sample universe. The solution to this problem is that a good field survey will also consider features that are outside the sample area. Even so, It is unlikely that unless the archaeologist is very lucky he or she will discover all the sites in the sample universe.
This lab illustrates the use of sampling strategies in an archaeological survey, but remember that the probabilistic sampling strategies presented above are independent of both survey methods and the archaeological field conditions. Sampling strategies are used by archaeologists in many other situations, including: site survey, site excavation, and artifact analysis. In all of these cases, even though the sample universe is different, the basic sampling strategies remain the same. Use your knowledge of sampling strategies to answer the following questions:
1. Looking at the illustration of all known sites and the illustrations of sampling strategies above, first comment on the types of sites that are most visible through sampling and the sites that are frequently missed. Then explain the differences. Remember that any probabilistic sample units are assigned according to idealized strategies that are independent of the archaeological field conditions.
2. You need to derive a representative sample of artifacts from a collection of archaic artifacts that contains lithics, groundstone, and ceramics. Which sampling strategy would you use to make sure that each type of artifact was equally well represented? Note that this question has nothing to do with field survey.
3. If you are working on a large Mesoamerican collection of ceramic artifacts which contains both plainware (unpainted) and painted vessels, and you are only interested in the painted vessels, which sampling strategy would you use? Note that this question has nothing to do with field survey.
4. What are the two probabilistic sampling strategies that you could use if you wanted to ensure that sample units were dispersed across the your entire sample universe?
5. Which sampling strategy would you use in a field survey in which you already have documentary evidence of the position of the site that interests you?
6. Of the probabilistic approaches outlined here, which would you think is the least useful to the archaeologist engaged in a field survey of the region in western Montana illustrated in this lab? Explain why.
|*Title illustration modified from an image in Field Methods in Archaeology: Seventh Edition, Hester et al. Mayfield Publishing Co., 1997.|