j. Cosmet. Sci., 54, 367-378 (July/August 2003) Scalp hair length. II. Estimating the percentages of adults in the USA and larger populations by hair length CLARENCE ROBBINS and MARJORIE GENE ROBBINS, Clarence Robbins Technical ConsMting, 12425 Lake Ridge Circle, Clermont, FL, 34711. Accepted for p•blication December 12, 2002. Synopsis Scalp hair length assessments by anatomical site, previously made in Florida theme parks on adults (1), are related to anatomical measurements to obtain estimates of free-hanging hair lengths in centimeters. A plot of the natural logarithm of the percent population versus these hair lengths provides a straight line and an equation that permits the estimation of the numbers of persons in the USA and larger populations with hair lengths up to 183 cm (just beyond ankle-length). Data were also collected via a literature search for even longer hair lengths (ankle-length or longer) to provide an equation to estimate the numbers of persons with exceptionally long hair. A comparative plot of these two equations suggests that "normal" anagen periods may be considerably longer than current estimates in the literature. INTRODUCTION In this paper, an attempt is made to estimate the percentages of persons in the USA and larger populations with different lengths of long hair, up to abnormally long scalp hair. This is an onerous task involving many assumptions, but we believe the data covering up to at least 183 cm (six feet) for the United States of America (USA) are relatively good approximations and that the percentage estimates for longer hair for the developed world based on the cited assumptions are also satisfactory. In a previous paper, hair length studies at four different theme parks in central Florida were described and used to estimate the percentages of persons in the USA with different lengths of scalp hair corresponding to different parts of the anatomy, e.g., the shoulders, the shoulder blades, the waist, and the buttocks (1). In the current work, the anatomical positions are related to anatomical measurements in order to estimate hair lengths from equations relating these anatomical measurements to the percentages for the populations of the USA, the developed world, and a population equal to that of the entire world. RESULTS AND DISCUSSION POPULATION The population on which these data are based is, strictly speaking, the population that 367

368 JOURNAL OF COSMETIC SCIENCE attends theme parks in Florida or in the USA. Several attempts were made to contact the Wait Disney Corporation to obtain information on that population. Those contacted refused to provide any information, indicating that such was proprietary. As indicated in Part I, the hair-length data were found to be from the same population (with regard to hair length) among all the different theme parks. Furthermore, comparison of the data to that from a 1972 hair-length market research survey in the USA among females ages 14 to 60 (geographically dispersed across the entire USA) indicated good agreement between the shoulder-length assessments (26.3% versus 24%). Table I shows a more complete comparison, with newer data, from only 601 females from the MGM Studio theme park, done in late 2000, evaluating short (chin-length), medium (chin-to-shoulder-length) and long (shoulder-length or longer) hair only. These data show reasonably good agreement. However, the theme park study shows a lower percentage of women with short hair (29% to 33%) and a larger percentage with long hair (30% to 24%). These differences could be due to either different populations, or to a change in hairstyles and hair-cutting practices for the more recent study, but are partly due to the small sample size of this study, because the sum of all the theme park data versus this USA study shows 26.3% versus 24% for the shoulder-length data (see Table I). It is our conclusion that the theme park study does provide a reasonable approximation for hair-length populations in the USA. The percentages provided by our theme park data most likely represent the mid-teenage group up to people in their mid-60s. We excluded those with an estimated height of less than 4.5 feet, and although many people age 60 and older attend theme parks, fewer people from this older age group attend theme parks than are in the general population of the USA. Therefore, the theme park data is more likely representative of the age group 15 to 60 than of the entire population, and so these data most likely provide slightly higher percentages for the long-hair groups than for the overall USA population. Additional calculations are provided to approximate hair length for the developed world (defined in Table II) and for the entire world. It is our conclusion that the estimates for the developed world will be better approximations than for the entire world because the age groups for the developed world are closer to those of the USA and of the theme park attendees and because the hair cutting practices will also be more similar (see Table II). ANATOMICAL POSITIONS AND HAIR LENGTH An important step in our current effort was to relate these anatomical positions (Table Table I Hair Length From Theme Parks Versus a I972 USA Study Percentage Hair length 1972 USA study* MGM study on women** All theme park studies*** Chin or shorter 33 29 -- Chin-to-shoulder 43 41 -- Shoulder or longer 24 30 26.3 * N = 15,000 women ages 14 to 60. ** N = 601 women, MGM Studios theme park. *** N = 12,150 women, several Florida theme parks.