A Comparison of Biface Reduction and Curation Indices

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Chapter 8

A COMPARISON OF BIFACE REDUCTION AND

CURATION INDICES

Rachel A. Horowitz Tulane University

INTRODUCTION

Currently several indices designed to measure biface reduction and

curation exist, but no information concerning their relationships or

comparability is known. As such, biface assemblages measured using different

indices cannot be compared, impeding the ability to perform integrative

studies concerning mobility and technological organization, especially among

assemblages dominated by bifaces.

Varying definitions of both reduction and curation exist, thus increasing

the difficulties in determining ways to quantify the two concepts. Reduction is

usually separated into two phases: production and use, with which curation is

usually associated. Many tools, however, are used and retouched continuously,

implying no concrete separation exists between the production and use phases

of tools. Hiscock and Attenbrow (2005) suggest that some tools are subjected

to almost continuous modification of morphology and no separation between

reduction and curation is possible. Therefore, the separation of reduction and

curation, and their respective quantifications, is difficult.

Shott (1996: 267) defines curation as ―the degree of use or utility

extracted, expressed as a relationship between how much utility a tool starts

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with its maximum utility- and how much of that utility is realized before

discard.‖ In other words, curation is a continuous alteration of materials and

the rate and degree of alteration vary in response to environmental conditions

(Nelson 1991). Since the utility of a tool changes throughout its use-life and

curation is connected with these changes, curation can be discussed as a

measure of the entirety of a tool‘s use-life. Most people refer to the rising

segment of the utility curve as reduction or production (to the left of the line in

Figure 8.1) and to the decrease from maximum utility as curation and use (to

the right of the line in Figure 8.1).

Figure 8.1. Utility curve over time as normally represented.

This model, however, does not consider multiple peaks of utility (Figure 8.2).

Which, when considered, suggest curation actually spans all stages of tool

production and use. As Andrefsky (2008) states, all tools are in various stages

of curation, it is simply that part of curation is commonly called production;

therefore, reduction cannot be arbitrarily divided between the production and

use phases of a tool. As curation covers the entire use-life of a tool and all

tools are in states of curation, studies concerning the reduction process of a

tool can also discuss curation. Additionally, reduction refers to the process

from the initial procurement of materials to the discard of the tool, the same

span considered by curation. As such, reduction and curation indices, although

often differentiated, are difficult concepts to separate. To alleviate this issue, in

this paper the indices will be referred to as measures of both reduction and

curation.

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Figure 8.2. Utility curve representing multiple peaks of utility.

In order to rectify the lack of comparability between biface assemblages,

this paper examines six indices of bifacial reduction and curation using an

assemblage of bifaces from the Great Basin Paleoarchaic period, which

corresponds chronologically to the terminal Pleistocene and early Holocene

(TP/EH) (11,500-8,000 RCYBP) (Beck and Jones 1997). Bifaces from four

assemblages, representing both quarry and habitation sites, in central and

eastern Nevada were analyzed (see Beck et al. 2002): Knudtsen 1 and 2,

Cowboy Rest Creek Locality 1 (CRCL1) and Locality 2 (CRCL2) and Little

Smoky Quarry (LSQ) (Figure 8.3).

Figure 8.3. Map of relevant sites in the Great Basin (Beck et al. 2002: 483).

The Knudtsen site and the CRC quarries are located in Grass Valley, while

LSQ is located in Little Smoky Valley. 122 bifaces from Knudtsen, 176 from

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CRCL1 and 2, and 290 from LSQ, for a total of 588 bifaces, were examined.

All bifaces were collected during investigations by Hamilton College. The

comparisons and evaluations of the indices should alleviate the present lack of

comparability of measures of biface reduction and curation.

THE INDICES

The goal of this study is to compare indices of biface reduction and

curation to determine the comparability of these indices. The comparison of

the different indices will determine whether the indices are measuring the

same thing and to see if data produced by one index can be compared with

data obtained from another. Six indices were chosen for examination:

Callahan‘s (1979) stages, the edge angle, the Johnson Thinning Index (JTI)

(Johnson 1981), a combination of Clarkson‘s (2002) Index of Invasiveness (II)

and Andrefsky‘s (2006) Hafted Retouch Index (HRI), the Ridge Count

Retouch Index (RCRI) (Wilson and Andrefsky 2008), and the edge offset.

These indices represent the three types of indices defined by Shott and

Weedman (2007): geometric, which consider how the plan of the tool changes

with use, allometric, which consider the relationship between the size and

shape of the artifact, and direct, which consist of original measurements of tool

size. As all three types of indices are discussed here, the relative benefits of the

different types of indices will also be discussed.

Biface Stages

The traditional method of measuring reduction is by application of a stage

classification such as the one described by Callahan (1979). Callahan created a

guide to generalized biface reduction using the edge angle and the ratio

between the width and thickness of the biface to make assignments to five

stage classes. The classification used in this study is a modification (see Beck

et al. 2002) of Callahan‘s (1979) stages. The modifications made by Beck et

al. (2002) result in four stages numbered zero to three. The definitions were

based on form, number and shape of flake scars, edge sinuosity, and thickness

(Table 1). The stages were measured on the bifaces by two analysts and the

resulting stage assignments of each biface were averaged, resulting in a total

of seven stages (see Beck et al. 2002). The averaging of the stage

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classifications was a result of disparities in the stage assignments. One of the

drawbacks of this index is that it is subjective in the different emphases placed

on various attributes by analysts. As Beck and Jones (1989) state, differences

in perception and emphasis can be a source of error in class assignments. As

such, clear definitions of the classes are necessary to limit such error.

Table 8.1. Biface stage characteristics (Beck et al. 2002: 494).

Stage Characteristics

0

Large biface with irregular shape and low symmetry; few very

widely and/or variably spaced flake scars; very wide edge offset

(very sinuous); very thick and irregular cross-section

1 Large biface with irregular shape; widely and/or variably shaped

flakes; wide offset; thick and irregular cross-section

2

Large biface with semi-regular and symmetrical shape; closely

and/or semi-regularly spaced flake scars; edge offset moderate;

cross-section semi-regular

3

Regular, symmetrical biface; closely and/or quite regularly spaced

flake scars (pressure flaking often present); offset close (little edge

sinuosity); cross-section thin and regular; later edge grinding

evident on haft

Edge Angle

One of the simple aspects used in Callahan‘s original stage classification

was the edge angle. The edge angle of a biface becomes more acute as the

production of the biface proceeds, as one goal of biface manufacture is to thin

the biface (Johnson 1981, Callahan 1979). Moreover, as production proceeds,

errors such as step fractures are removed, thus decreasing the overall edge

angle of the biface. Therefore, smaller edge angles should result from more

reduced bifaces and the average edge angle of a biface should decrease

through production and use. Similarly, the range of the angle should decrease

throughout production as bifaces become more uniform. Once a biface has

reached a stable thickness, further narrowing of the biface will cause the edge

angle to increase, particularly in instances when edge retouch flakes are not

very invasive.

The edge angle of the bifaces was measured using a goniometer. Angle

measurements were taken around the circumference of the biface at two

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centimeter intervals, so as to include any variation present. Broken areas,

caused either by production error or post-depositional processes, were

excluded from the measurements as they tend to have higher angles which

could increase the angle measure. The average angle and angle range for each

biface were then determined. A problem with the use of the edge angle as a

measure of reduction is that larger bifaces naturally have larger angle

measures due to the greater thickness of the biface (Johnson 1981). Problems

may result from this index in the comparisons of bifaces of varying sizes.

Thinning Index

As stated above it is generally accepted that thinner bifaces represent later

stages in production. Johnson (1981) states that one of the aims in producing a

biface is to maintain the width while reducing the thickness of the tool. He

points out, however, that larger bifaces are naturally thicker than smaller ones,

a difference which must be compensated for when measuring the reduction of

the biface. Johnson (1981) developed the Johnson Thinning Index (JTI) as a

method to compensate for natural size differences. The JTI uses the weight of

the artifact divided by the plan view area to determine a measure of reduction

and curation and is measured in grams per centimeters squared. The JTI

should decrease through the production and use of the biface due to the

thinning and loss of mass caused by the production, use, and retouch of the

biface. The measurements used here were performed for the study presented in

Beck et al. (2002).

Retouch Invasiveness Index

Indices of invasiveness are also valid ways of measuring biface reduction

and curation. Two such indices are Clarkson‘s (2002) Index of Invasiveness

(II) and Andrefsky‘s (2006) Hafted Retouch Index (HRI). These indices

measure the density of retouch as a proxy for tool curation. The retouch flakes

are an effort to increase the utility of the tool (Andrefsky 2006). With use, a

tool is dulled and becomes less efficient, signifying a drop in the potential

utility of a tool and indicating the necessity of retouch. To return an edge to

sharpness, retouch is applied. As the number of retouch flakes increases, its

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level of curation rises. Given this relationship between retouch and curation, a

measure of invasiveness of retouch flakes would be a measure of curation.

Clarkson‘s index evaluates the concentration of retouch along an edge.

The biface is divided into 16 segments, eight on each side, providing a

measure of the proportion of an edge that has been modified by retouch. The

face of a biface is divided into two zones, an outer zone along the perimeter of

the biface and an inner zone. If flakes are present in the outer zone, a value of

.5 is assigned to that section. If a flake extends into the inner zone, a value of 1

is assigned; if no retouch flakes are present, a score of 0 is assigned (Figure

8.4). The curation value of the biface is determined with the formula II=

ΣSs/16, where Ss is the segment scores (Clarkson 2002). Clarkson (2002)

claims the index should only increase with increasing amounts of retouch, as

flake scars cannot be removed. In experimental studies, the II demonstrated an

increasing curvilinear relationship with instances of retouch (Clarkson 2002).

Figure 8.4. Index of Invasiveness, A: the division of the biface into segments; B: the

assignment of values to each of the segments (Clarkson 2002: 67).

The HRI was specifically designed to measure curation of hafted bifaces.

The biface is divided into 16 segments, eight on each side, excluding the haft

section. Scores of 0, .5, and 1 were assigned to each segment depending on the

percentage of retouch flakes in the segment (Figure 8.5). If no retouch flakes

are present, a score of zero is assigned. If half the segment is covered by

retouch flakes then a score of .5 is assigned. If only retouch flakes are present,

the score is 1. The curation value is determined with the formula: HRI= Σ Si/n,

where Si is the sum of all segment scores and n the total number of segments

(Andrefsky 2006). The HRI assumes biface retouch is performed to increase

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the utility of the tool. Therefore, if more retouch is present, the tool is more

curated. In experimental studies, the HRI increased through various episodes

of retouch, but not at a uniform rate; the HRI was less sensitive to the later

episodes of sharpening (Andrefsky 2006).

Figure 8.5. Hafted Retouch Index; shows the division of the biface into segments

(Andrefsky 2006: 746).

The II and the HRI differ in minor details. For this study they were

combined with slight modifications (Combined Index of Invasiveness (CII))

(Figure 8.6). In the CII the biface was divided into 16 segments and the

midpoint of each section was determined.

Figure 8.6. Combined Index of Invasiveness, A: the divisions of the biface, B: values

assigned to the segments.

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Values of 0, .5, or 1 were assigned depending on the presence of flake scares

and if they extended past the midline of the segment. Scores of 0 are assigned

if no flakes are present in the segment. Scores of .5 are assigned if flake scars

exist but do not extend past the midline of the segment. Scores of 1 are

assigned when the scars extend over the midpoint of the section. The CII is

determined using the formula: CII= Σ Si/n, where Si is the sum of all section

scores and n the total number of segments.

The CII is an adaptation of the II and the HRI to measure bifaces in all

stages, including those in the production stage. The index should still function

as invasiveness of flakes changes throughout the production of a biface.

However, the relationship between the use-life of the biface and the CII value

will probably not be linear. For instance, early stage bifaces usually have large

biface thinning flakes that reach or pass the midline of the biface, thus

covering many segments of the tool. In such instances, a biface would be

assigned a high value for the index. As the biface nears completion increasing

numbers of less invasive flakes are removed along the edges for shaping,

resulting in a decrease in the index score. With use and retouch, the level of

curation would rise again, but probably not to the level of the production

bifaces. Retouch on tools tends to be focused along the edges and the flakes

tend to be less invasive than early production flakes.

To expedite the process of measuring the CII templates were created by

tracing bifaces onto graph paper and measuring the sections and their

midpoints. The templates were transferred to transparencies so they could

easily be placed on the bifaces with the guidelines visible. Although the

method may produce errors in that the guides are not specific to each artifact,

leading to circumstances where the sections and midline are not exact for the

tool, it proved to be the most efficient manner for measuring the CII.

Additional variability in index scores comes from the subjectivity of the

index. The analyst must determine whether flake scars that fall into two

segments will be counted in one or both segments. The decision could increase

or decrease the measure of curation of the biface. In this study, flake scars that

fall into two segments are assigned a value in only one segment, the one from

which the flake originated, and the other segment(s) was assigned a score of

zero, unless another flake scar was present. Comparisons between assemblages

would be affected by this issue unless standardized.

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Ridge Count Retouch Index

In an adjustment of Clarkson‘s (2002) II to encompass biface production,

Wilson and Andrefsky (2008) created a Ridge Count Retouch Index (RCRI).

They found that the II assigned high levels of curation to bifaces in early

stages of production. Therefore, they felt a manner of measuring biface

reduction that would encompass both the production and use phases of

reduction was necessary. The RCRI is an estimate of the number of flake scars

on the surface of the biface and is based on the observation that the number of

flake scars increases as production proceeds, as more flakes are removed from

a biface. Rather than counting flake scars, the Wilson and Andrefsky (2008)

index samples the number of flake scars using the number of ridges on the

surface of the biface.

The RCRI divides bifaces into eight segments on each side, as seen in the

CII. Six one by one cm squares were placed on the grid, three on each side of

the biface. The squares are placed in the same location for the measure of all

bifaces (Figure 8.7). The use of standardized boxes ensures equivalent

amounts of surface area are tested on each biface. The number of dorsal ridges

in each square is counted, summed, and divided by six to determine the

average ridge count for each biface (Wilson and Andrefsky 2008).

Figure 8.7. Ridge Count Retouch Index Schematic: shows the location of the analyzed

sections of the bifaces, the 1x1 cm squares, demarcated by the dotted lines (Wilson and

Andrefsky 2008: 97).

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Once again, templates for measuring the RCRI were formed by tracing

bifaces onto graph paper, measuring the section divisions, and placing the

boxes in the locations specified by Wilson and Andrefsky (2008). The

templates were transferred to transparencies so they could easily be placed on

the bifaces with the guidelines and boxes visible. Bifaces of differing sizes

were used as models to attempt to ensure measurements would not be affected.

Wilson and Andrefsky (2008) determined, using experimental studies, that

the number of ridges on bifaces increased until resharpening began. They

attribute the decrease in ridges at this point to the type of hammer used in the

study. The decrease in ridges was associated with a change from hard hammer

to soft hammer percussion. Changes in hammer type and density can affect the

manner in which flakes are removed from a tool, causing the RCRI to be

sensitive to the hammer type used in biface reduction. Flakes removed using

soft hammer percussion tend to be large, flat, and thin (Whittaker 1994),

which would remove large areas of the surface, thus erasing evidence of

previously removed flakes. Wilson and Andrefsky (2008) also mention that

variation in the reduction levels of individual bifaces can be explained by

material flaws or knapping error, which might cause a large portion of the

biface surface to be removed, thus erasing previous flake scars.

Variability in the index might result from the sample size of the surface

area of the biface measured. In some cases, the selected areas might have

fewer ridges than found on other parts of the biface, indicating the biface was

in an earlier stage of reduction than in actuality. Further variability could be

caused as the proportion of the surface area measured on bifaces of varying

sizes differs. On a biface with a surface area of six cm2, three cm

2 on each side,

100% of the biface surface is examined. If the biface has a surface area of 30

cm2, 15 cm

2 on each side, only five percent of the biface is examined.

Therefore, smaller bifaces have a more realistic representation of the number

of ridges present than larger bifaces. Wilson and Andrefsky (2008) do not

address the issue of sample size in their index, but from the experimental

results it appears as though the index values are stable at the current sample

size. For bifaces with a surface area less than six cm2

total, or less than three

cm2 on each side, this index cannot be applied. An increase in the number of

boxes in which ridges were counted would decrease the variability of surface

area percentage but would also further limit the number of bifaces which could

be measured using this index. Increasing the number of boxes could also lead

to situations of over-counting ridges, where the same ridge appears in more

than one box, thus skewing the RCRI value.

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Further complications for this index could result from the difficulties in

determining the number of ridges present on the surface of the biface.

Depending on the material from which the biface was made ridges are more or

less obvious. For instance, ridges can be seen more easily on obsidian than on

fine grained volcanics (FGV). Physical and chemical weathering can obscure

traces of ridges, amplifying the difficulty of identifying the number of ridges

on the surface of a biface. Application of this index to an archaeological

assemblage should determine if this is a serious drawback to the use of the

RCRI.

Edge offset Index

The edge offset index measures the sinuosity of the edge of a biface, a

characteristic included in Callahan‘s (1979) stage assignment qualities; in

other words it measures the displacement of the edge from a straight line

(Schmidt 2006). Callahan (1979) suggests the sinuosity of the biface edge

should decrease throughout the reduction process as the biface becomes more

uniform (Figure 8.8). Stork (1997) employed a measure of edge sinuosity and

states sinuosity decreased as bifaces were reduced. Early stage bifaces are

more sinuous due to the depth, spacing, and uneven size of flake scars present

on the edges. Throughout reduction, bifaces become more uniform, thus

decreasing the edge sinuosity. Stork (1997) measured the offset of the edge

simply as the width of the area of maximum edge displacement.

Figure 8.8. The decreasing sinuosity of the edge through reduction (Callahan 1979).

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In order to quantify the edge offset of the biface, scans were taken of each

edge of the biface using a flatbed scanner. Two parallel lines were then drawn

on the scan, one on each side of the line representing the edge at the locations

of maximum displacement on each side. The lines were drawn to align with

the apex and trough of the curve. The distance between the two lines was

measured at several points along the curve, especially in areas of high

variation. The maximum, minimum, and average displacement for each biface

were determined by calculating the average and maximum and minimum

values of the series of measurements. The measurements used in this study

were performed by Schmidt (2006), so the sample size for this index is only

127 bifaces.

One issue facing the measurement of the edge offset is that the scanning

of the edge of the biface may lead to distortion. As the edge of a biface is

rarely flat, the edge does not lie evenly on the scanner surface, which might

cause distortion. Additionally, measuring the index is fairly laborious due to

the number of measurements that must be taken (Schmidt 2006).

RESULTS AND ANALYSIS

Presently, reduction and curation levels measured with different indices

cannot be compared (Kuhn 1990). This study should provide evidence as to

whether it is possible to compare levels of reduction and curation measured

with alternative indices. As the study compares both discrete (stage

assignments) and continuous (edge angle, JTI, CII, RCRI, and edge offset)

measures of reduction and curation, a comparison can be made as to whether

the two types of measures provide the same information. Shott (1996) suggests

curation is a continuous process, signifying that a continuous variable should

be a better manner of quantifying reduction and curation. Also, the edge angle,

edge sinuosity, and RCRI are direct measures, the JTI an allometric measure,

and the CII a geometric measure, allowing comparison of the three types of

indices suggested by Shott and Weedman (2007).

Stage Assignments

The biface stage assignments are difficult to analyze both quantitatively

and as an individual index. Despite these difficulties, it appears as though the

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stage assignments are an adequate measure of the level of reduction and

curation of bifaces. This index partitions variability in biface morphology

based on the critical goals of biface manufacture: thinning, symmetry, and the

linearity of the edge (Whittaker 1994, Callahan 1979). As such, more uniform,

and thus more finished, bifaces are classified as later stage bifaces than more

variable bifaces in early stages of production. As a classification based on the

goals of biface reduction, the stage assignments are a valid measure of

reduction and can be further used to evaluate the other indices.

Continuous Indices

With the continuous indices, it is easiest to see trends in terms of the stage

assignments, which divide the sequence of reduction. The JTI, as stated above,

is expected to have a decreasing linear relationship with the stage assignments

due to the thinning of a biface as reduction proceeds. When evaluated in terms

of the stage assignments, the mean JTI decreases across these assignments. In

fact, the JTI has an indirect-curvilinear relation (Figure 8.9) with the stage

assignments. The index is curvilinear as it is more sensitive to the earlier

stages of biface production than it is to later stages and retouch. The thinning

of a biface, which is what the index measures, occurs predominately in those

early stages, making the index more sensitive to those stages. Despite the

decrease in sensitivity, the standard deviation of the index continues to

decrease throughout the process of reduction (Figure 8.9).

Figure 8.9. Boxplot of the JTI by stage assignment.

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The edge angle was also predicted to decrease throughout the process of

reduction, and hence decrease across the stage assignments. In early stages,

bifaces could be unevenly thinned or be suffering from production problems,

such as step-fractures, which would lead to high variability in the angle

measures. Both the average angle, which was predicted to decrease due to the

thinning of later stage bifaces, and the angle range, which should decrease

with the increased uniformity of bifaces, were examined. The average angle

remained fairly consistent, with a slight decrease at stage one (Figure 8.10).

The lack of variation of the average angle across the stages is surprising as

bifaces earlier in production tend to be larger, which affects the angle, and also

tend to be thicker, which should also result in a larger edge angle. The angle

range generally decreased, but with a few areas of increasing value.

Figure 8.10. Angle range and average across the stage assignments.

The patterns demonstrated by the angle range and average can be

explained through an examination of the process of biface reduction. The

slight increase in the range between stages 0 and .5 might simply be a result of

the averaging of the stage measures or could be due to early flaking which

occurred along the edge of the biface. The decrease in the angle range from

stages .5 to 2 would be a result of the thinning occurring on the biface, which

should reduce the edge angle. The increase between stages 2 and 2.5 might be

explained through edge retouch and shaping. As stated earlier, retouch and

shaping can increase the edge angle, as the width of the biface decreases and

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non-invasive flake scars create a steeper edge angle. With this explanation, the

angle range is shown to be more sensitive to changes that occur in the later

stages of production and use than the JTI. However, with only the angle

measurements, it would not be possible to differentiate between bifaces with

slightly larger angles which were in earlier stages of production and those

angles which were more obtuse due to shaping and retouch. Therefore,

although the edge angle is a sensitive index, it is not a particularly useful

measure of reduction and curation as the value of the index is not unique

across the reduction sequence.

The CII was expected to have a non-linear, perhaps U-shaped relationship,

with the stage assignments. However, no clear pattern across the stages seems

to exist (Figure 8.11). Although this index was created specifically to deal with

biface retouch, not production, as was measured here, the index should still

distribute in a patterned way as a biface moves through manufacture. The CII

seems highly problematic, due not only to the inconsistent results in this study,

but also to the difficulties in applying the index. The index appears to be

largely subjective in its application, despite efforts to add consistency to its

application.

Figure 8.11. CII in terms of stage assignments.

The RCRI was expected to generally increase across reduction stages as

seen in the experimental study (Wilson and Andrefsky 2008). In fact, the

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RCRI did generally increase across the stages with the exception of between

stages 0 and .5, when there was a marked decrease (Figure 8.12).

Figure 8.12. RCRI across stage assignments, showing relative sample size (circles) and

one standard deviation (stars).

This decrease is not significant due to the standard deviation at these areas. As

such, the RCRI demonstrates that more flake scars are present on a biface as

the stage of reduction increases. One caution that should be associated with

this index is that, for the most part, the bifaces examined in this study were of

similar or the same materials, so, any differences associated with the varying

difficulty in counting ridges on bifaces of different materials are not accounted

for in this study.

The edge offset index was expected to decrease throughout the stage

assignments as the biface became more uniform. Upon examination of the

maximum, minimum, and average offsets, the edge offset generally decreases,

although with some variability (Figure 8.13). The maximum, minimum, and

average edge offset all decrease except between stages 1 and 1.5 and 2 and 2.5

when there is a slight increase. The reason for the slight increase at this stage

is unknown, although it could be an issue of sample size. For this index, the

sample size for the early and late stages is smaller than that in the middle

stages. The general decreasing trend of the index was expected as bifaces tend

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to become more uniform throughout production, thus decreasing the variability

and sinuosity of the edge. Although the measurement of this index can be time

consuming, it seems to act consistently across the stage assignments.

Figure 8.13. Maximum, minimum, and average edge offset in terms of the stage

assignments.

In terms of relationships between the continuous indices, the only indices

that demonstrate a significant correlation are the average edge offset and the

JTI (R2: .588) (Figure 8.14). The lack of correlation of the JTI and the RCRI is

unusual, as a negative correlation would be expected between these indices

since both seem to be effective measure of reduction and curation. The lack of

correlation between the indices does not negatively impact the effectiveness of

these indices as measures of reduction and curation.

Figure 14. Scatterplot of the average edge offset and the JTI.

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DISCUSSION AND CONCLUSION

The goal of this study was to examine measures of bifacial reduction and

curation in order to determine the effectiveness and comparability of different

indices. If the measurement of reduction and curation levels of bifaces is more

uniform and comparisons between assemblages are possible, integrative

studies concerning lithic assemblages from different localities and those

analyzed by different individuals could be performed.

From the relationships between the varying indices and their distribution

across the stage assignments, it is demonstrated that some of the indices better

measure the reduction continuum than others. The stage assignments provide a

basic manner for separating bifaces, but have some analytical limitations as it

is a discreet index.

In terms of the continuous indices, several of those examined here are not

at all useful for measuring reduction or curation. The CII is not sensitive to

any stage of the reduction continuum, although it might be useful for bifaces

that have been used and retouched. This aspect of the CII was not investigated

here. The angle range is a sensitive index, but the measurement of the index

does not provide a manner of differentiation between bifaces with higher angle

ranges due to shaping and retouch and those with higher ranges in earlier

stages of production. It is not a particularly useful index for measuring

reduction and curation.

The JTI is a useful index for the measurement of reduction and curation as

it is easily measured and is differentiable across the reduction sequence. The

only drawback of this index is that it becomes less sensitive in the later stages

of reduction, so the JTI is more useful for assemblages dominated by early

stage bifaces, such as those found at quarry sites, than it is for assemblages

dominated by later stage bifaces.

The average edge offset decreases fairly consistently across the reduction

continuum. At a few stages, however, the average edge offset increases, which

could lead to similar problems as the angle range: that it is difficult to

differentiate between earlier and later stage bifaces with similar measurements.

As the index correlates with the JTI, an effective measure, the average edge

offset should also be an effective measure of reduction and curation. When

used with caution, the average edge offset is a useful indicator of reduction

and curation levels.

At first glance the RCRI seemed to be an extremely subjective index with

difficulties in defining the precise aspects of the biface to be measured, but

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upon examination of the results, the RCRI increases steadily across the

reduction continuum. It does not correlate with any other index, and a negative

correlation with the other indices would be expected. Despite the lack of

significant correlations, the RCRI appears to be a valid method for measuring

reduction and curation.

The stage assignments, average edge offset, the JTI, and the RCRI are the

four measures of bifacial reduction and curation discussed here that are most

useful for measuring reduction and curation. Each is a different type of index;

the stage assignments are a discrete index, and the others are all continuous

measures. The RCRI and the average edge offset are direct measures and the

JTI an allometric measure. Since each of these indices functions as an estimate

for the reduction and curation levels of bifaces, it appears that both discrete

and continuous indices as well as direct and allometric indices are viable types

of indices for determining bifacial reduction and curation. Variation found in

different indices reflects the quality of the indices themselves and not the type

of index.

In addition to determining which indices were effective measures of biface

reduction and curation, the relative comparability of effective measures was

also an aspect of this study. Due to the lack of significant correlations between

continuous indices, it appears as though comparisons of assemblages measured

with different indices would be ineffective. The JTI and average edge offset do

correlate significantly, but comparisons between the two would be difficult

due to the differing scales of the two indices. At this point it seems as though it

is impossible to compare assemblages measured with different reduction or

curation indices.

Of the four indices described here which effectively measure reduction

and curation each has different strengths and weaknesses. Depending on what

is being studied, a different index should be chosen, or as Eren and

Prendergast (2008) suggested, analysts should determine what question they

wish to answer before choosing an index. For some analyses, a discrete index

might be more useful, so the stage assignments should be employed. For

quarry assemblages, the JTI would be most useful. The RCRI should not be

used on an assemblage with many small bifaces, as the index would not be

applicable to many of the bifaces.

Despite the lack of correlation between indices, and the difficulties in

comparing different indices of biface reduction and curation, such indices are

still important tools in lithic analysis. Indices provide an objective measure of

the level of production or use that a biface has experienced. As such, studies

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Rachel A. Horowitz

which employ these measures are less subjective, and through the use of

indices future studies can employ published data from other assemblages in

integrative studies. Such integrations of data are more difficult when using

subjective measures of the stage of production or level of use of a biface.

This study has related the process of measuring and the drawbacks and

advantages of six indices used to measure bifacial curation and reduction. Four

of these indices are viable indicators of different levels of reduction and

curation. Through the use of these indices, the study of biface curation and

reduction should be simplified. Additionally, through the methods described

here, a more uniform method of applying these indices is established, which

will increase the comparability of biface assemblages examined by different

analysts. The increased comparability should contribute to the use of biface

reduction and curation in the study of tool use, the organization of technology,

and mobility.

ACKNOWLEDGMENTS

Many thanks to Nathan Goodale and Tom Jones for their advice,

assistance, and guidance while I was writing my senior thesis, from which this

paper comes. Thanks also to Grant McCall, Lisa Fontes, Jessica Wheeler, and

Erlend Johnson for their comments.

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Documents

A Comparison of Biface Reduction and Curation Indices