Anthropometry, Osteometrics, and Osteometric Boards

Anthropometry, and osteometrics within this domain, centers on methods for measuring the human body, including the skeleton, and has been used since the early eighteenth century for various research purposes in biology, biological anthropology, and related fields (Jamison and Zegura Reference Jamison and Zegura1974; Marks Reference Marks2012, Reference Marks2017). Eighteenth- to mid-twentieth-century anthropometric research in biology and biological anthropology was primarily typological and focused on racial classification and the estimation of intelligence levels and criminal tendencies (Marks Reference Marks2012, Reference Marks2017). Although these domains have primarily shifted from classificatory to evolutionary approaches to human phenotypic variation, including metric variation, many biological anthropologists continue to collect and analyze anthropometric data, including osteometrics. Among other applications, skeletal metric data—especially maximum length measurements of elements within the appendicular skeleton (i.e., long bone lengths)—are commonly used to reconstruct maximum living stature, as well as growth and development patterns, and to estimate sex and age-at-death (e.g., Adams and Byrd Reference Adams and Byrd2002; DiGangi and Moore Reference DiGangi, Moore, DiGangi and Moore2012; Moore Reference Moore, DiGangi and Moore2012; Moore and Ross Reference Moore, Ross, DiGangi and Moore2012). Therefore, osteometric boards are one of the most-used data collection devices in biological anthropology, including osteology, bioarchaeology, paleopathology, and forensic anthropology.

Since their development in the late nineteenth century, traditional osteometric boards have not changed substantially in design and construction (Hepburn Reference Hepburn1899; Schiller Reference Schiller1992). Paul Broca (1824–1880), a French physician, anatomist, and anthropologist, developed the first osteometric board in 1888 (Schiller Reference Schiller1992). Hepburn (Reference Hepburn1899:111) described Broca's original design as “a flat graduated board or plank, at one end of which a flat vertical upright is fixed. Against this upright part the bone to be measured is placed, while to the opposite end of the bone a right-angled triangle of wood is applied, and the length of the bone is read off up on the graduated plank.”

Adjustments to this original design have been minimal; traditional osteometric boards consist of a single board base with a fixed panel and detachable sliding panel. An object is placed between these to determine its length. Hepburn (Reference Hepburn1899) added stabilizing elements, which increased the ease of measurement observations; this adjustment also reduced inter- and intraobserver errors generated using Broca's design (Hepburn Reference Hepburn1899).

In the twentieth century, adjustments to the traditional osteometric board were intended to make it more user-friendly, portable, and affordable. For example, some commercially available versions—Carolina Supply Company, Paleo-Tech (now produced by France Casting)—are collapsible, making them more suitable for transport and field-based data collection. Noncommercial, craft-produced versions of traditional osteometric boards also feature limited adjustments. For instance, the Abawerk osteometric board has two upright panels along the length and width of the board with metric-ruled paper placed on the base; the paper is used to generate length measurements for skeletal material placed on the board (Geise Reference Geise1986). This board design was intended to make measurement generation easier for observers while increasing its accuracy: the ruled paper can be measured from multiple angles, although it is less durable than standard osteometric board materials, such as wood, metal, and plastic (Geise Reference Geise1986). Indeed, many researchers forego the expense of commercially manufactured osteometric boards—which range from $75 to $1,100, with the majority retailing for more than $200 USD—by making craft versions of osteometric boards, some of which have more durable designs than others (Figure 1). For example, Naples and colleagues (Reference Naples, Breed and Miller2010) created an inexpensive osteometric board for classroom use, with the goal of facilitating student usage and offering more opportunities for learning forensic methods. Made of rulers, tape, glue, and cardboard, this version of a traditional osteometric board is very affordable but not particularly durable, and the fragility of its components and construction may generate intra- and interobserver error rates that are unsuitable for research use.

FIGURE 1. Traditional, museum-grade wooden osteometric board (A) with a sliding panel (B).

Metric Considerations

Reliability, validity, and considerations of inter- and intraobserver error are vital to anthropometry and osteometrics. Reliability refers to the measure of inter- and intraobserver error, in which an object is measured on two different occasions by at least two different observers, with little random error (Nance Reference Nance and Aldenderfer1987). Validity is the degree to which a measurement consistently accomplishes its intended purpose. In other words, it is a question of how accurately the measurement generated using an osteometric board reflects the true length of the skeletal element, when measuring from a baseline that is accepted as accurate (Nance Reference Nance and Aldenderfer1987). Accuracy refers to how close the measurements are to a true value (i.e., the baseline value). This type of information must be collected methodically because of human error—both inter- and intraobserver—instrumentation issues, and the observer's experience level.

Inter- and intraobserver variation is especially critical to consideration of anthropometric, including osteometric, data. Interobserver error results from inconsistent measurements by different observers, whereas intraobserver error results from inconsistent measurements taken by a single observer (Adams and Byrd Reference Adams and Byrd2002). Generally, interobserver error is greater than intraobserver error (Langley et al. Reference Langley, Jantz, McNulty, Maijanen, Ousley and Jantz2018). Fewer errors also typically occur in the generation of measurements of maximum length and breadth measurements of skeletal material than in other standard skeletal measurements (Langley et al. Reference Langley, Jantz, McNulty, Maijanen, Ousley and Jantz2018). Notably, acceptable error rates for anthropometry are <1.5% for intraobserver error and <2% for interobserver error (Perini et al. Reference Perini, de Oliveira, Santos Ornellas and de Oliveira2005). Postcranial measurements commonly considered as being “difficult” for most observers to generate, such as those of the tibia (e.g., maximum length vs. medial and lateral condylar length), should have less than a 3% error rate (Adams and Byrd Reference Adams and Byrd2002).

Importantly, error rates within skeletal measurements recorded using osteometric boards, whether traditional or novel (e.g., PODv1), can be reduced through observer awareness of external factors such as humidity that can affect measurement precision and accuracy, and thus the reliability and validity of the measurements, along with consequent adjustments in practice: the observer's lack of awareness of these factors leads to measurement errors attributable to the device, observer, or both (Langley et al. Reference Langley, Jantz, McNulty, Maijanen, Ousley and Jantz2018). Some factors are external to and independent of the observer, some are observer- and device-specific, and some represent a combination (Albrecht Reference Albrecht1983; Geise Reference Geise1986; Langley et al. Reference Langley, Jantz, McNulty, Maijanen, Ousley and Jantz2018). For example, humidity can substantially affect measurements generated using the Abawerk osteometric board. Giese (Reference Geise1986) found that elevated relative humidity of 60% and higher in the local environment in which data recording occurred made the grid paper expand and changed a given measurement's outcome between 0.5 and 1.0 mm. Overall, as ambient humidity increased, so did the length of the measurements (Geise Reference Geise1986).

Observer-specific factors include the observer's level of experience in collecting skeletal metric data using an osteometric board (traditional or novel), which can influence reliability. Adams and Byrd (Reference Adams and Byrd2002) assessed reliability relative to observer experience level in postcranial metric data collection. In their study, participants in the 52nd annual American Academy of Forensic Sciences meeting with varying levels of experience (0–1 year, 1.1–5 years, 5.1–10 years, and 10+ years) in recording postcranial skeletal metrics used both digital calipers and an osteometric board to record 22 postcranial measurements. They found that less-experienced observers—with experience of five years or less—generated measurements with higher interobserver error. At the same time, they found that complacency and overconfidence among observers from every experience level also generated imprecision. Commonly observed measurement and data recording errors included transposing numbers, decimal place errors, failure to “zero out” the digital calipers prior to data collection, transcription errors, and confusion surrounding established procedures for generating standard skeletal metrics (e.g., Adams and Byrd Reference Adams and Byrd2002; Buikstra and Ubelaker Reference Buikstra and Ubelaker1994; White et al. Reference White, Black and Folkens2011).

Reliability and replicability are fundamental to osteometrics (Adams and Byrd Reference Adams and Byrd2002; Langley et al. Reference Langley, Jantz, McNulty, Maijanen, Ousley and Jantz2018). One way to enhance these two factors is to restrict analyses to osteometric measures that do not require extensive observer experience, such as maximum length measurements (vs. pubis length). These “easier” measurement types have lower error possibilities, helping decrease inter- and intraobserver errors in their collection (Adams and Byrd Reference Adams and Byrd2002). However, restricting methods in this fashion can also greatly limit the scope of analyses featuring osteometric data. Another way involves a variety of improvements to the devices used for collecting osteometric data so that they produce more consistent measurements, which can include using computer-assisted methods (Adams and Byrd Reference Adams and Byrd2002; Harris and Smith Reference Harris and Smith2009). Our work represents the latter approach.

Osteometric Laser: Preliminary Study

The PODv1 used in this study was developed from preliminary testing of an initial model that generated laser measurements using a direct ToF method (Anderson and Osterholtz Reference Anderson and Osterholtz2021). ToF is a method for measuring distance by determining the time it takes for photons to travel between a sensor and an object (Koerner Reference Koerner2021). Anderson and Osterholtz (Reference Anderson and Osterholtz2021) assessed whether maximum length measurements of two cast replicas of long bones—femur, radius; Bone Clones, Human Male Skeleton, Disarticulated (SCM-192-D)—generated using a Bosch Blaze GLM 50 C laser measure (Bosch laser) were comparable to those generated with a portable PaleoTech osteometric board. Twenty volunteer observers from the Department of Anthropology and Middle Eastern Cultures at Mississippi State University (MSU), with varying levels of educational attainment in anthropology—for example, a BA degree in progress, MA degree in progress, PhD attained—and levels of experience in collecting osteometric data, collected maximum-length measurements from each element in one round.

A Pearson R test revealed a significant positive correlation between both device measurements of the radius (r = 0.597, n = 20, p = 0.005) and the femur (r = 0.988, n = 20, p = 0.04), indicating that the measurements from the two devices were in general agreement. Even though these results indicate a significant correlation, there was a difference between the radius (moderate, r = 0.597) and femur (strong, r = 0.98) correlation strength taken from the Bosch laser and the PaleoTech osteometric board. This was likely due to interobserver error associated with different levels of observer experience, which was potentially exacerbated by the absence of any instruction to them on established practices for collecting the measurements of these elements. Additionally, the initial model was not anchored to a table or a board, meaning that it and the Bosch laser had some instability, much like Broca's original device. This likely caused some variation within the measurements compared to the PaleoTech board. Although Anderson and Osterholtz (Reference Anderson and Osterholtz2021) showed that further refinements were needed, the results did indicate that the initial model and the direct ToF method had potential for generating some types of osteometric data comparable to a traditional osteometric board. Here, we build on this preliminary research. Specifically, testing the PODv1 addresses the technical issues identified in the preliminary research through several design modifications, using volunteer observers with consistent experience levels, and consistently providing standardized, detailed instructions on the correct use of both the traditional osteometric board (i.e., the PaleoTech) and the PODv1 in generating the maximum length measurements for each skeletal element included in the study.

Portable Osteometric Device

The PODv1 was developed to solve some of the reliability and validity issues that researchers observed with osteometric data collection using traditional osteometric boards. The PODv1 is operated by a rechargeable battery, and its results are generated through 3D printing.Footnote ¹ To measure the length of skeletal elements, it uses a laser-distance–measuring sensor module with direct ToF technology and with a transmitter and a receiver. Whereas traditional osteometric boards use a board to enable measurement of an object's length, in the PODv1 the board is entirely absent. Instead, laser sensors with ToF technology are used to measure distance; that is, the length of an object. The transmitter fires a laser pulse that is reflected off an object (e.g., the sliding panel) and then captured by the receiver to measure photon travel time (Koerner Reference Koerner2021). The laser-distance–measuring sensor used in the PODv1 has an accuracy of ±1 mm, depending on the lighting conditions and distance being measured (AliExpress 2022). Importantly, to achieve an error rate of less than 2%, the laser pulse in ToF distance must reflect from an object with greater than 73% reflectivity (AdaFruit 2016; Jans et al. Reference Jans, Green and Koerner2020). Therefore, for increased reflectivity and thus increased reliability, the PODv1 features a white filament target area, giving an 88% reflectivity (AdaFruit 2016).

Compared to traditional osteometric boards (e.g., PaleoTech; see Figure 1), the PODv1 is smaller in size and has a more open design, without an anchoring base board. The open design enables the PODv1 to generate measurements of materials ranging in length from 0.03 m to 2.00 m. This means that it can be used to generate maximum length measurements of skeletal elements spanning the full spectrum of human variation, as well as of other materials such as artifacts that are potentially recovered from field sites where the PODv1 is in use. Additionally, the PODv1's dimensions are approximately 115 × 100 × 58 mm, which makes it more portable and easier to store than traditional osteometric boards, even collapsible versions.

The PODv1 has two primary components and a straightforward setup. The first, a laser panel, is an upright panel containing the laser, the control unit, and the clamp stabilizer. The second component, the sliding panel, has a foldaway sliding stabilizer and stores the parts for the clamp stabilizer (Figure 2). The PODv1 is set up by assembling the clamp stabilizer and attaching it to the laser panel to create a 90-degree angle, which is then placed against a table (or similar flat surface) with a corresponding 90-degree angle. Next, the clamp stabilizer secures the PODv1 to the table with a clamp. After the PODv1 is secured to a table, the sliding panel is assembled and placed against the table. Then, the skeletal material (or other object for measurement) is placed against the laser panel. the sliding panel then secures the material, and the measurement generated is displayed on an LCD screen (Figure 3).

FIGURE 2. PODv1, including (A) the front portion of the Laser Panel with the laser on the right side, the control unit on left side of the Laser Panel (yellow box), the laser (yellow arrow), (B) the Sliding Panel with foldaway Sliding Stabilizer on right side, and (C) the Clamp Stabilizer storage on the back of Sliding Panel.

FIGURE 3. LCD screen on PODv1 including (A) Live Measurement display screen, (B) Precision Mode, and (C) Calibrate and History.

Portable Osteometric Device Features

The PODv1 has four different operating functions: Live Mode, Precision Mode, Calibration, and History. Only the Live and Precision Modes are used to measure the length of an object. The Live measurement is automatically engaged after turning the PODv1 on and displays a continuous measurement. This mode displays an active 25%, midpoint, and 75% of the measured object (see Figure 3A). It also displays the last Precision Mode measurement taken under the Live measurement reading (Figure 3A). The Precision Mode takes 20 measurements and displays their average (Figure 3B). The Calibration function recalibrates the device, returning it to zero. For recalibration to occur, however, a 100 mm block, which is incorporated into the design, must be placed between the two panels during calibration. The History function shows the last five Precision Mode measurements (Figure 3C).

Volunteer Observers

Volunteer observers (N = 45) were recruited from MSU (n = 23) and from participants in the 2022 American Association of Biological Anthropologist (AABA; n = 22) conference.Footnote ² A power analysis, consisting of a paired t-test with an alpha = 0.05 and power = 0.80, determined the minimum sample size to be 34 observers. This test was performed using GPower (3.1). IRB approval was obtained prior to data collection (MSU IRB-21-457). Volunteers at both MSU and the AABA were required to have completed an undergraduate or graduate-level human osteology course, whether at MSU or a previous degree-granting institution, or possess equivalent experience, such as lab work or taking part in a bioarchaeological field school, prior to data collection. Everyone was given written instructions and watched a six-minute video (made by the first author), both of which provided the same set of detailed instructions on how to use both the PODv1 and the Paleo-Tech Lightweight Field Osteometric Board. Additionally, each volunteer was given written and pictorial instructions for collecting measurements of the four bone elements. These instructions directly followed the procedures described in “Data Collection Procedures for Forensic Skeletal Material 2.0” (Langley et al. Reference Langley, Jantz, Ousley, Jantz and Milner2016). Langley and coworkers’ guide was used because it provides clear, detailed, and user-friendly instructions on how to collect the four measurements used in this study.

The first author proctored the volunteer observers at MSU, and the third and fourth authors proctored those at the AABA; the only assistance proctors provided was initially calibrating the PODv1 and assisting any volunteer who had difficulty operating either or both devices. After watching the video and reading the instructions, each volunteer observer independently assembled and operated each device. Each used both devices to measure the four skeletal elements in each of three consecutive rounds. In sum, each observer collected measurements on each element six times for a total of 24 measurements per observer. Volunteer observers entered each measurement into a Microsoft Excel spreadsheet. To limit bias and maintain anonymity, each volunteer recorded their measurements, number of years of experience using traditional osteometric boards, and their primary field of study (e.g., bioarchaeology, forensics). Experience level was categorized into three groups: novice, intermediate, and expert. The novice group incorporated those who had less than 3 years of experience with traditional osteometric boards, members of the intermediate group were those with 3–10 years of experience, and the expert group was made up of those with 10 or more years of experience. No other personal information was recorded (Supplemental Table 1).

Baseline Measurements of Skeletal Elements

We selected the four skeletal elements used in this study—femur, tibia, humerus, and ulna—to represent the spectrum of difficulty involved in collecting osteometric data for each, including maximum length. The tibia is considered to be difficult to measure because of its complex epiphyseal morphology (e.g., intercondylar tubercles; Adams and Byrd Reference Adams and Byrd2002), whereas the femur and humerus are not hard to measure, given their simpler epiphyseal morphology. The ulna lies between them; although it is not considered to be difficult to measure (Adams and Byrd Reference Adams and Byrd2002), its distinct epiphyseal morphology—olecranon and styloid processes—can create challenges for observers seeking to measure its maximum length.

The first, third, and fourth authors created the baseline skeleton measurement for each of the four bone elements—tibia, femur, humerus, ulna—drawing from two sources. At MSU, the authors generated baseline measurements for, and the volunteer observers collected measurements from, four complete dry bone elements representing four adult individuals from within the Đurđevac-Sošice Commingled Collection,Footnote ³ which is curated at MSU. This collection was chosen due to its accessibility, the permission granted by the descendant community for inclusion of the remains within research contexts, and the completeness of the selected skeletal elements. For the AABA volunteers, the authors generated baseline measurements for, and the volunteer observers collected measurements from, four cast skeletal elements drawn from two adult individuals (male, female) in the MSU Biological Anthropology teaching collection: Bone Clones, Human Female Skeleton, Disarticulated (SCM-191-D) and Human Male Skeleton, Disarticulated (SCM-192-D). Both baselines were generated using the same Paleo-Tech Lightweight Field Osteometric Board. Each author collected the measurements from each element in three rounds. All the measurements for each element were then averaged to create a baseline, true measurement for each element, both dry bone and cast. The baseline measurement for each element was then compared to the measurements generated by the volunteer observers at MSU and the AABAs using the PODv1 and the PaleoTech osteometric board, respectively, to test interobserver error and validity. Statistical analyses were completed using RStudio Statistical software.