Anthropology

Research Proposal: Visual Determination of Sex From the Human Scapula

Introduction

The goal of this project is to test a method for visual determination of sex from the human scapula discovered by Skelton (1978). A large sample of scapulas of known sex will be scored using the Skelton method and the accuracy of the method will be evaluated. The working hypothesis is that the Skelton method is able to identify the correct sex of scapulas with a rate of success that is significantly higher than chance alone. This hypothesis may be accepted if we can reject the null hypothesis that accuracy of the Skelton method is equal to the accuracy expected by chance alone.

The determination of sex from the skeleton is an important concern for osteologists and forensic anthropologists who base their analyses on data obtained from examination of skeletal material. The pelvis is thought to be the best part of the skeleton from which to determine sex, and the skull the second best (Bass, 1971), but in many cases the skull and/or the pelvis are missing from a skeleton and the ability to determine sex from an alternative anatomical region would be useful. The ability to determine sex from the scapula may also be useful in situations where the sex determined from the pelvis or skull is uncertain. In 1978 I undertook a study of metrical and visual methods for sex determination of the scapula (Skelton, 1978). I am, therefore, familiar with the existing methods of sex determination for this bone and with the bone's anatomy. During the 1978 study I proposed a set of visual criteria which seemed to be useful for determining sex, and subsequent informal observations have convinced me that this method is worth pursuing further. I have an earned doctorate in physical anthropology and have worked as a staff osteologist or consulting osteologist on several archaeological projects during the past twelve years.

Materials and Methods

I plan to test the Skelton method for visual determination of sex from the scapula using a sample of at least 50 male and 50 female scapulas. A suitable skeletal collection is housed at the Lowie Museum of Anthropology, University of California, Berkeley. Permission to use the skeletal collection will have to be obtained from Frank Norrick, Curator of the museum. The following information will be recorded for each scapula:

1. Specimen identification number.
2. Sex as determined from the pelvis using the method of Phenice (1969).
3. The angle that the axis of scapular breadth makes with the axis of maximum scapular length. This angle should approach 90 degrees in females, but be closer to 60 degrees in males. [Note: I should have included a diagram or illustration of this and the following characteristics. I didn't, in order to save space. Do include illustrations in your proposal].
4. Sub-glenoid concavity. The axillary border of the scapula should be concave in females, but straight in males.
5. Relationship between the tip of the coracoid process and the superior angle. When the scapula is placed in anatomical position the tip of the coracoid process should be inferior to the superior angle in females, but superior to the superior angle in males.
6. Shape of the glenoid fossa in cross section. The glenoid fossa should be deep when viewed in cross section in females, but shallow in males.

The condition of the scapula for characteristics 3 through 6 above will be recorded as hypermasculine (2), masculine (1), ambiguous (0), feminine (-1), and hyperfeminine (-2). A contingency table will then be constructed for each characteristic that compares sex and score for that characteristic. These contingency tables will have the form shown in figure 1. For each characteristic, a chi-square test will reveal whether there is a non-random distribution of scores by sex. An overall score will be obtained for each specimen by adding the scores for each of the 4 characteristics that are shown to have a non-random distribution by sex from the chi-square test. If the overall score is greater than zero, then the specimen will be diagnosed as male. If the overall score is less than zero, then the specimen will be diagnosed as female. These diagnoses will be compared to the known sex of the specimen and each diagnosis will be recorded as correct or incorrect. The null hypothesis that the frequency of correct diagnoses is equal to 50% will be tested.

Data collection should take one week at the Lowie Museum of Anthropology, University of California, Berkeley, CA.

Implications of this Research

If the Skelton method for visual sex determination from the scapula is more accurate than expected by chance, then this method would be a useful addition to list of sex determination methods available to an osteologist. If the method is no more accurate than chance, then the human scapula can be considered uninformative for sex using visual methods.

References Cited

Bass, William M., 1971. Human Osteology: A Laboratory and Field Manual of the Human Skeleton. Missouri Archaeological Society, Columbia, MO.

Skelton, Randall R., 1978. Sexing the scapula: Various methods. Paper prepared in satisfaction of the "Substantive Research Paper Requirement" for the M.A. degree in Anthropology, University of California, Davis.

Phenice, T. W., 1969. A newly developed visual method of sexing the Os Pubis. American Journal of Physical Anthropology 30: 297-302.

Other References

Bainbridge, Douglass. and Santiago Genoves Tarazaga, 1956. A study of sex differences in the scapula. Journal of the Royal Anthropological Institute of Great Britain and Northern Ireland 86:109-134. Hrdlicka, Ales, 1942a, The scapula: Visual observations. American Journal of Physical Anthropology 29:73-94.

Hrdlicka, Ales, 1942b, The adult scapula: Additional observations and measurements. American Journal of Physical Anthropology 29:262-415.

Stewart, T. D., 1954. Sex determination of the skeleton by guess and by measurement. American Journal of Physical Anthropology 12:385-392.

Budget

• Equipment: Digital Calipers $142.95
• Travel: Air fare: Missoula to San Francisco $378.32
• Bus fare: Daily, 5 days (@$2/day) $10.00
• Lodging: 5 days at Motel 6 Berkeley (@32.95/day + 8.25% tax) $164.75
• Food: 5 days at $16 per diem $80.00

Total: $776.02

Research Proposal: Visual Determination of Sex From the Human Scapula

Introduction

The goal of this project is to test a method for visual determination of sex from the human scapula discovered by Skelton (1978). A large sample of scapulas of known sex will be scored using the Skelton method and the accuracy of the method will be evaluated. The working hypothesis is that the Skelton method is able to identify the correct sex of scapulas with a rate of success that is significantly higher than chance alone. This hypothesis may be accepted if we can reject the null hypothesis that accuracy of the Skelton method is equal to the accuracy expected by chance alone.

The determination of sex from the skeleton is an important concern for osteologists and forensic anthropologists who base their analyses on data obtained from examination of skeletal material. The pelvis is thought to be the best part of the skeleton from which to determine sex, and the skull the second best (Bass, 1971), but in many cases the skull and/or the pelvis are missing from a skeleton and the ability to determine sex from an alternative anatomical region would be useful. The ability to determine sex from the scapula may also be useful in situations where the sex determined from the pelvis or skull is uncertain. In 1978 I undertook a study of metrical and visual methods for sex determination of the scapula (Skelton, 1978). I am, therefore, familiar with the existing methods of sex determination for this bone and with the bone's anatomy. During the 1978 study I proposed a set of visual criteria which seemed to be useful for determining sex, and subsequent informal observations have convinced me that this method is worth pursuing further. I have an earned doctorate in physical anthropology and have worked as a staff osteologist or consulting osteologist on several archaeological projects during the past twelve years.

Materials and Methods

I plan to test the Skelton method for visual determination of sex from the scapula using a sample of at least 50 male and 50 female scapulas. A suitable skeletal collection is housed at the Lowie Museum of Anthropology, University of California, Berkeley. Permission to use the skeletal collection will have to be obtained from Frank Norrick, Curator of the museum. The following information will be recorded for each scapula:

1. Specimen identification number.
2. Sex as determined from the pelvis using the method of Phenice (1969).
3. The angle that the axis of scapular breadth makes with the axis of maximum scapular length. This angle should approach 90 degrees in females, but be closer to 60 degrees in males. [Note: I should have included a diagram or illustration of this and the following characteristics. I didn't, in order to save space. Do include illustrations in your proposal].
4. Sub-glenoid concavity. The axillary border of the scapula should be concave in females, but straight in males.
5. Relationship between the tip of the coracoid process and the superior angle. When the scapula is placed in anatomical position the tip of the coracoid process should be inferior to the superior angle in females, but superior to the superior angle in males.
6. Shape of the glenoid fossa in cross section. The glenoid fossa should be deep when viewed in cross section in females, but shallow in males.

The condition of the scapula for characteristics 3 through 6 above will be recorded as hypermasculine (2), masculine (1), ambiguous (0), feminine (-1), and hyperfeminine (-2). A contingency table will then be constructed for each characteristic that compares sex and score for that characteristic. These contingency tables will have the form shown in figure 1. For each characteristic, a chi-square test will reveal whether there is a non-random distribution of scores by sex. An overall score will be obtained for each specimen by adding the scores for each of the 4 characteristics that are shown to have a non-random distribution by sex from the chi-square test. If the overall score is greater than zero, then the specimen will be diagnosed as male. If the overall score is less than zero, then the specimen will be diagnosed as female. These diagnoses will be compared to the known sex of the specimen and each diagnosis will be recorded as correct or incorrect. The null hypothesis that the frequency of correct diagnoses is equal to 50% will be tested.

Data collection should take one week at the Lowie Museum of Anthropology, University of California, Berkeley, CA.

Implications of this Research

If the Skelton method for visual sex determination from the scapula is more accurate than expected by chance, then this method would be a useful addition to list of sex determination methods available to an osteologist. If the method is no more accurate than chance, then the human scapula can be considered uninformative for sex using visual methods.

References Cited

Bass, William M., 1971. Human Osteology: A Laboratory and Field Manual of the Human Skeleton. Missouri Archaeological Society, Columbia, MO.

Skelton, Randall R., 1978. Sexing the scapula: Various methods. Paper prepared in satisfaction of the "Substantive Research Paper Requirement" for the M.A. degree in Anthropology, University of California, Davis.

Phenice, T. W., 1969. A newly developed visual method of sexing the Os Pubis. American Journal of Physical Anthropology 30: 297-302.

Other References

Bainbridge, Douglass. and Santiago Genoves Tarazaga, 1956. A study of sex differences in the scapula. Journal of the Royal Anthropological Institute of Great Britain and Northern Ireland 86:109-134. Hrdlicka, Ales, 1942a, The scapula: Visual observations. American Journal of Physical Anthropology 29:73-94.

Hrdlicka, Ales, 1942b, The adult scapula: Additional observations and measurements. American Journal of Physical Anthropology 29:262-415.

Stewart, T. D., 1954. Sex determination of the skeleton by guess and by measurement. American Journal of Physical Anthropology 12:385-392.

Budget

• Equipment: Digital Calipers $142.95
• Travel: Air fare: Missoula to San Francisco $378.32
• Bus fare: Daily, 5 days (@$2/day) $10.00
• Lodging: 5 days at Motel 6 Berkeley (@32.95/day + 8.25% tax) $164.75
• Food: 5 days at $16 per diem $80.00

Total: $776.02