The IQR and MAD norm methods are inefficient with skewed datasets, and specific methods exist for these circumstances e. However, with human oxygen isotope data, we do not consider skewness to be problematic as the underlying population is highly likely to be normal and skewed data may well indicate a sample with outliers. Kaminaljuyu has a smaller range 6. The two methods produce different estimates of outlier numbers at Kaminaljuyu. The dataset has a tail to the positive side of the distribution but the question is, which of these values deviate significantly enough from the underlying population as to represent outliers?
Visual inspection does not make it clear how many outliers there are.
The statistical methods tell us that 9 from 1. This is different from whether the numbers of outliers seem reasonable from an archaeological perspective, however, in general, whether the sample has 9 or 11 outliers out of a sample size of 90 is unlikely to have a meaningful impact on archaeological interpretations.
There are, however, situations where neither of these methods is appropriate. In such a case simple statistical methods applied at the population level are unlikely to be able to produce meaningful estimates of outliers. In summary, we suggest that the 1. Using these methods is not difficult: In studies combining two isotopic systems, e. Our assessment of oxygen isotope studies globally reveals that there is great disparity in the distribution of human oxygen isotope analyses across the world Fig 5.
As with many archaeological distribution maps, this reflects archaeological research, in terms of excavation, bioarchaeologists and publication, rather than the reality of past population distribution.
A large number of sites in Europe have been analysed, and a fairly large number of studies from the Americas. Sites in Africa, Asia and Australasia are poorly represented. Even within Europe, the data are biased with the UK being very well-represented with relatively few studies conducted in the rest of Europe Fig 6. This limits our understanding of the past and highlights the need for more archaeological research in these under-studied regions.
Thus, when converted to boundaries to delimit outliers, there is a large degree of isotopic overlap regardless of how the data are divided i. Fig 9. There are two potential reasons for this large degree of overlap, and it is likely that both contribute to the problem.
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Firstly, that human behaviour and physiology lead to large ranges of oxygen isotope values in populations with access to the same drinking water source s. Secondly, that the sites studied so far in Europe are in areas with similar precipitation oxygen isotope values mostly between -9 and It stands to reason that if the precipitation values are similar then the human values will also be similar. These two problems combined make the application of oxygen isotope studies to Europe difficult, at least in terms of the areas of Europe that have been studied to date: This has implications for the application of the technique not just in archaeology, but also in forensics and ecology.
It would be very interesting to analyse individuals from the south coast of Iberia or northern Scandinavia in order to characterise the full extent of variation that one could expect in human oxygen isotope values within Europe. Nevertheless, there is some cause for optimism.
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With a large sample size, small yet significant differences in mean isotope values have been found between groups of individuals from east and west Britain, showing that isotopic differences exist across relatively small geographical areas [ 46 ]. Even with the low coverage of data across Europe discussed here, there are areas that have distinct isotope values in the full dataset: This would suggest that the technique should work best in areas, such as the Alps and northern Scandinavia, which have distinct precipitation oxygen isotope values compared to the surrounding regions, given a sufficient sample size.
The reasons for this large variation likely include physiological factors, human modification of drinking water, importation of food and drink, and the use of multiple sources of water with different oxygen isotope values. When using statistical techniques, both sample size and the choice of statistical method have a profound effect on the number of outliers identified. We recommend the use of both the 1.
Care should be taken when using statistical methods where the sample size is less than Researchers should recognise that there is a trade off between sensitivity to outliers and false positive or negative identifications, as well as a degree of subjectivity in the identification of real anomalies significantly interesting deviations amongst the noise.
All statistical results should be considered in the light of common sense: All isotopic data are best interpreted in conjunction with all other available evidence, including archaeological and osteological evidence, and complementary isotopic data e.
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Parsimonious explanations are to be preferred so as not to present unrealistic scenarios. Given the large oxygen isotopic variation within archaeological human samples, the limited amount of geographic variation in precipitation oxygen isotope values is challenging. The results presented here show that if one considers a single result from a European individual it is not possible to determine where in Europe that individual is from, as the European regions analysed to date cannot be distinguished solely on the basis of oxygen isotope values.
Given this conclusion, any attempt to identify the specific potential homeland of identified migrants is inadvisable.
In most circumstances, however, knowing that an individual has migrated a long distance is sufficient to answer the archaeological question posed. When there is other archaeological information to suggest a potential homeland for migrants see, for example, [ 55 ] , stable isotope analysis can refute, but not confirm, such a hypothesis. Despite these difficulties human oxygen isotope data do, in general, show correlations with geographical parameters.
The technique is not fundamentally flawed per se—it is more that the typical variation in human oxygen isotope values is larger than has usually hitherto been assumed. In summary, statistical techniques can help to identify first-generation migrants from oxygen isotope analysis of an archaeological sample.
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However, securely identifying migrants is not straightforward. Unless there have been a significant number of previous analyses in an area, each sample should be treated as an individual dataset and in most cases identification of a homeland should not be attempted. Criteria of each method range, 2SD, 1. For some of methods, there are multiple curves apparent for sample sizes between 5 and We would like to thank the Dorothy Garrod Isotope Group in Cambridge, for their discussion of the points addressed in this article.
We are grateful to Dr Luca Bondioli and the three reviewers for very useful comments that improved the paper. Copyright Esri. All rights reserved. Click through the PLOS taxonomy to find articles in your field. Abstract Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. April 28, Copyright: The authors have no support or funding to report.
Introduction Oxygen isotope analysis is an increasingly popular tool to study past human migrations, and has now been applied to samples from many time periods and locations [ 1 — 3 ]. Background Oxygen isotopes from precipitation to the body Oxygen isotopes in mammalian tissues reflect the isotope values of the water ingested as water or from food at the time of tissue formation [ 7 ]. He said talks were going on between Irda and theme park operators from Australia, Indonesia, Japan, Europe and North America to set up their theme parks in Iskandar Malaysia.
He said that the company was in the midst of talks to buy a piece of land, between To date, UMLand's landbank stands at BB Waterfront owns Thomson Iskandar, a medical hub project located on 1. Co-located with the hospital is an outpatient medical centre that will contain clinic suites. In less than an hour, still shrouded in semi-darkness, the Singapore-bound traffic leading to the 1. A striking number of family sedans with Singaporean licence plates stream steadily toward the expressway that leads to the heart of the island republic. Inside the cars, bleary-eyed schoolchildren contemplate the long day ahead.
For this alone, Singaporeans are prepared to face the daily routine of waking up at 4am in order to get their children to school on time, and then waiting until 7pm for all family members to have finished work or extracurricular activities before driving across the causeway again. As the population of Singapore increases and the cost of living, especially of housing, remains high, more Singaporeans are choosing to live across the narrow strait in Malaysia and commute.
The traffic is a visible sign of reinvigorated links between the two countries, whose relationship has been punctuated by political tensions despite shared historical roots and huge bilateral trade. As Singapore celebrates the 50th anniversary of its independence — and separation from Malaysia — the rivalry between the two neighbours seems finally to be giving way to a greater recognition of their interdependence. Last month, the front page of the widely read Today newspaper featured a lavish spread highlighting the growing trend of Singaporean families relocating to Iskandar, the 2,sq km special development zone in the southern Malaysian state of Johor.
Until , the two countries were part of the same union, first under British colonial rule and then under the fledgling state of Malaysia. The huge number of people now travelling between Malaysia and Singapore is a fresh reminder of just how close the two countries fundamentally are. Malaysians have for many years been relocating to Singapore in search of job opportunities and higher salaries.
Now it is Singaporeans who are searching for a gentler pace of life in Malaysia. In moving across the causeway, both peoples are giving the lie to the prejudices of recent decades by reaffirming links between their cultures that go back centuries. The homes being built in the Forest City project would add to the nearly , new residential units that are in the pipeline for the rest of Johor state.
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The large number of new homes coming up in Johor has raised concerns in Singapore. Minister for Culture, Community and Youth Lawrence Wong, who is a board member of the Monetary Authority of Singapore, told Parliament on Monday that the nearly , new private residential units are more than the total number of private homes in Singapore. Supported by ample space and relatively lower costs across the Causeway, that strategy has seen much development taking place in Johor over the years - to the point that analysts have lately flagged the prospect of a glut in certain sectors.
For example, Maybank Investment Bank warned that the pro-perty oversupply in Iskandar is "likely to get worse before it gets better".
Given Singapore's close ties with its neighbour, it's in the nation's interest to see Iskandar Malaysia - formerly known as Iskandar Development Region and South Johor Economic Region - succeed over the long term. Singaporeans are building, among other things, a medical hub, an international school and factories in the sprawling economic zone about three times the size of Singapore. A number of small and medium-sized enterprises are looking to locate there to take advantage of lower labour and land costs. And Singaporeans with money to buy a second residential property have been wooed by developers of condominiums and landed property in Johor.
The government of Johor plans to unveil new laws which will restrict foreign home buyers to new international zones to protect locals from being priced out of the market. According to Datuk Abdul Latif Bandi, Johors Minister for Local Government and Housing, details of the plan will be released in June or in August in order to get feedback from the property industry and the public prior to making a final decision. The move follows complaints that thousands of residential units built by developers are primarily targeted at foreigners.
The units, which include three-storey landed homes and luxury condominiums, are often priced way beyond the reach of most Johoreans.