Another guest post from our esteemed guest blogger, David Pettegrew, the co-director the Pyla-Koutsopetria Archaeological Project and the 2010 Cyprus Research Fund speaker. Be sure to check out his posts on Tuesday and Wednesday.
When I announced my plans to conduct a survey experiment where we would “vacuum” an entire 40 x 40 m unit, Dimitri and Bill both laughed and told me that I had to try it simply for its absurdity. The 40 x 40 m survey unit was our standard size for the 252 units that we laid out across the Koutsopetria plain . As far as survey units go, 40 x 40 m (or 1,600 square meters) is a relatively small unit compared to that typically employed by those who conduct distributional survey. At the same time, when on the group, 40 meters is still vast when compared to the dimension of most lived space. After all, a 40 x 40 meter unit is over 130 square feet on a side and over 17,000 square feet which makes a single survey unit much larger than even the most over-sized suburban McMansions. The reason that my suggestion was humorous, however, had to do with the method I proposed for collecting artifacts. In our typical pedestrian survey, we only looked at 20% of the surface of the unit (for a more reasonable and suburban 3,400 square feet) and only collected each unique artifact from what we saw on the surface. My proposal was more extreme: get down on our hands and knees and completely “vaccum” (or “hoover”) all the artifacts from 100% of the unit to produce an exhaustive (and exhausting!) total collection rather than a quick 20% sample.
Why? I had the suspicion that the amount of artifacts we see when we walk across the unit is but a fraction of the total number of artifacts actually on the ground. The suspicion was based on experiments conducted in 2004 & 2006 where we ‘vacuumed’ artifacts from a 5% sample of our 40 x 40 m units, producing on average artifact counts that were 4 times greater than that produced through our 20% sample using pedestrian survey. We also proved through these experiments that the substantially larger number of artifacts did not really contribute much new chronological or functional information that warranted the additional investments of time and energy. We published a report on those experiments in an article by the authors in the Report of the Department of Antiquities, Cyprus 2007. However, we were aware of the substantial fluctuations of artifacts within 40 x 40 m units and the risk of a 5% sample (80 sq m) being unrepresentative of the unit as a whole (1600 sq m). The point of our 2010 experiments, then, was to test the results with a much more robust sample. While I initially wanted to vacuum 100% of the unit, time constraints prohibited me to vacuuming 25% of the unit. Even still, 25% of the unit is 5 times greater than what we sampled in 2004 and 2006.
Due to the limited time for fieldwork this season (and time constraints were one of the reasons that we sampled the units to begin with!), we could only resurvey a single unit placed in the highest-density area immediately northeast of the excavated apse of the early Christian basilica. We picked this unit to overlap with our very first Discovery Unit, a grid square of 40 x 40 m surveyed in 2004 northeast of the enclosed excavated part of the site of Koutsopetria. We divided the 40 x 40 unit into sixteen 10 x 10 m subunits, each representing 6.25% of the overall unit area (1,600 sq m). The grid squares have been given the prefix of G followed by a number between 1-16, as the following plan shows.
In our interest in comparing artifact counts noted during pedestrian survey—where a surveyor walks across the unit examining a 2 m wide swath and counting all pottery, tile, lithics, and other artifact types—with the total population of artifacts actually on the surface, we implemented two stages to the experiments. The first stage (pedestrian survey) we will report on today.
We began by having four fieldwalkers walk across the unit, recording all artifacts visible in their swath, giving a 20% sample of every 10 m of space across a 40 m transect. We collected ‘sub-tract’ artifact counts every 10 meters to produce density figures for each of the subunits (G1-G16) and assess the fluctuating density of pottery, tile, and lithic artifacts within a survey unit.
We collected the data for pedestrian survey three times. The results of these three separate pedestrian survey exercises are shown in the four figures below. The numbers represent artifact counts of each type (pottery, tile, other, and total), and the gray shaded columns with orange numbers represent the total artifact count for the swath per fieldwalker.
The first time (see figure 1.1 below) a group of untrained students walked the units—Andrew, Luke, Valerie, and Zane—who who had only seen artifacts at the museum and not in their "natural" (or better, archaeological) contexts.
A steady light rain the following day provided the chance for these same students to rewalk the unit a second time (see figure 1.2 below) with artifacts slightly more visible as a result of the washing of the dust.
Finally, a group of experienced fieldwalkers—David Pettegrew (DKP), Dimitri Nakassis (DN), and Bill Caraher (WRC) —walked the unit and counted artifacts (see figure 1.3).
Hence, the variables in these three episodes of pedestrian survey were experience, and, to a lesser extent, the amount of dust and dirt obscuring the surface of the pottery. Otherwise, between episodes environmental factors were constant, as were methodological factors and figure 1.4 shows the average of all the counts produced.
We walked these units on June 9 and 10 and each took between 15 minutes and half an hour.
Comparing simply the total artifact counts (the bottom right grid within each of the outlined figures), it is interesting to note that the rain appears not to have made a difference overall in density counts between units [1.1] and [1.2]. Although one student count went up significantly after the rain (LHM: 118 243), and another student count was slightly greater (AMH: 200 241), VAW’s total counts were essentially unchanged (335 to 334), while ZRB’s total counts actually declined (238).
As far as the other variable (experience) goes, there were some significant disparities between experienced walkers and inexperienced walkers as evident in counts for particular grid squares (compare G1 for [1.1] and [1.3]). Otherwise, the overall artifact counts were comparable for the units: the lowest-density and highest-density subunits occurred between all three walking episodes. If we look at total artifact counts for each unit as a whole, students counted 942 artifacts in [1.1] and 1056 artifacts in [1.2] while experienced walkers counted 940 artifacts in [1.3]. That is remarkably close!
We noticed one major difference, however, in the “other” category, which includes all artifacts besides pottery and tile: marble revetment, gypsum, shell, ancient glass, and ground stone agricultural implements. The experienced field walkers noted 2-4 times the number of other artifacts in [1.3] than inexperienced fieldwalkers in [1.1] and [1.2]. An experienced walker counted 4 lithic artifacts (chipped stone & ground stone) in G3 and G7 that an inexperienced walker missed.