Differentiate between Non-probabilistic sampling and Probabilistic sampling in Archaeology,

         The term Archaeology has been differently by different Authors. For example, Harley and Jones (2004) maintained that, “Archaeology is a discipline concerned with studying the past using physical evidence in conjunction with other types of historical sources such as documents, Maps, Illustrations, Photographs and Oral history”. Furthermore, another scholar called Staeck (2002: 2) who defined Archaeology as “The study of old things of the past, the common theme in all of Archaeology is that part of information comes from the material remains of the past. The actual people made, used and altered and then left behind. Also these remains are collectively called material culture.

        Sampling as well, has been spoken by various scholars to explain what exactly is that mean. For stance, Grant, J (2008:436) described that, “Sampling is the careful selection of an Areas to investigate or material to analyse, usually based on mathematical probability to ensure that, what is selected is representative of wider evidence”. So, in Archaeology Sampling is a process of selecting an area for excavation in the particular Archaeological site, thus the selected samples becomes representatives of the entire area so as to collect data available.

        Therefore, Archaeological sampling  is concerned with examining a portion of archaeological  record  under study that is a region ,site or stratum .We do sampling because ,it is impossible to sample entire universe of the study, as said by one of the Scholar called Jim Grant (2008: 10),he argue that “Whatever deposited is fragmented of the past  materials ,a variable of this portion of these deposit will survive .So archaeologists will recover sample of these ,that is because not every site can be filled walked  ,let alone excavate and hence the choices have to be made”.

       Fagan (2002), also outlined that, There are two ways to approach sampling which are Non probabilistic sampling and probabilistic sampling ,.The later ,refers to archaeological sampling method based on formal statistical criteria in selecting sample units to be investigated ,these sample are selected randomly by lottery methods or random number methods. Each unit area has equal chance to be selected .Probabilistic sampling includes simple random sampling, systematic random sampling and stratified random sampling.

       Also, Staeck (2002), Defined non-probabilistic sampling as the sampling procedure which doesn’t afford any basis for estimation has an equal chance of being included in a sample .Thus, in archaeology, it is archaeologists preference to select area to be excavated .This method is also known as purposive sampling, judgemental sampling and deliberately sampling.

       According to Kothari (1990), categorized Probabilistic sampling in various kinds as described below;

      Simple random sampling; this refers to probabilistic sampling in which the selection of the areas for survey and excavation is done completely on the basis of random selection. All areas for survey and excavation are selected randomly and they have an equal chance.

       Systematic random sampling in Archaeology involves the selection of the areas for survey and excavations at regular intervals or order, but it starts with random selection and proceed with systematic procedures in selecting areas for survey excavation.

        Stratified random sampling; This is also a probabilistic sampling in which Archaeological sites is divided into various zones known as strata, Then, in each stratum unit area is selected for survey and excavation or few strata can be selected to represent other strata. This depends on the sample size, work force and money that an Archaeologist has.

      Though those methods seek a portion of archaeological record to be investigated, they differ in the following aspects;

      Time involved, whereby Non-probabilistic sampling is done at short time this is because the decision on where to excavate is based on personal preference but in probabilistic sampling time taken is high because archaeologists have to take measure of surveyed area such as to divide into grid squares, quadrants and transects .These activities need enough time. This is to say, in probabilistic sampling especially stratified sampling takes more time where by you have to divide archaeological site into zones or strata and then you select the area for excavation from each stratum while in non-probabilistic, time wastage is minimal since the area for excavation is known and no many processes are needed.

       Provision of information, in such a way that Non-probabilistic sampling provide contextual information about an areas, features or site that means a more intensive survey is done and features are identified  such as the location of mound sites, and features of landscape are noted.

         Then, probabilistic sampling is more expensive than non-probabilistic sampling during survey and excavation. This is due to the fact that, probabilistic sampling in Archaeology needs more team work, big area to be sampled. This aspect needed for survey and excavation unlike probabilistic sampling which depends on personal preferences.

        Also ,the aspect of bias cannot be undermined as a part and parcel of differences between probabilistic and non-probabilistic sampling in Archaeology, where by Non probabilistic sampling is based on personal judgements since archaeological records could lead to bias in which a certain types of evidence (sample) can be neglected  and others over represented into sample ,but in probabilistic sampling involve  division of universe into units have an equal chance to be included into sample and so increase the efficiency of the technique. The point is supported by Staeck (2002:118) where he stated that, “probabilistic sampling has minimal bias because the selection of units for excavation is done randomly where by each unit has equal chance to be chosen, for example strict random sampling places units across a site without relying on any excavator biases” this is different to non-probabilistic sampling which has a lot of bias since personal preferences is more considered.

         In probabilistic sampling also, each unit area have an equal chance to be selected in the sample simply because the selection of unit area is done for excavation is done randomly .But in Non probabilistic because it based on personal preference to select archaeological units which not all units can selected in a sample. So, these methods are very important to archaeologists due to the fact that most of archaeologists surveys are large, that impede archaeologists to study the entire universe because of limited money and time. Because of such difficulties, archaeologists select representatives from a universe to be included in a sample.

    Then, in probabilistic sampling, there is a great chance of getting insufficient Archaeological remains or information this is because it relies much on random selection of the area to be excavated. As result, the selected unit areas may contain insufficient information, but in non-probabilistic sampling, the selection of the area for excavation is done purposely. Therefore an Archaeologist knows well the existence of Archaeological information in a certain area where he/she wants to survey and excavate, thus enough Archaeological information may be obtained.

      All in all, Archaeological sampling is crucial despite of the differences they have, and this is due to the fact that both probabilistic and non-probabilistic are intended to seek for the Archaeological information for the reconstruction of historical records of particular cultural remains which will be excavated after the whole process of sampling to be completed.

REFERENCES

     Colin Re Frew and Paul Balum (1996) Archaeology theories, methods and practice,2^nd London ,Thames and Hudson L.t.d.

     Fagan, B.M (2004) Ancient lives, An introduction to Archeology and pre-history, 2^nd ed. New jersery; Pearson prentice Hall.

     Grant et al (2008) The archaeology course book ‘’ An introduction to themes ,sites, methods and skills, 3^rded, USA and Canada, Routledge publishers.

     Harley and Jones (2004) an introduction to historical archaeological “revealing the past”  2^nd ed, New South Wales, NSW heritage office Sydney museums.

    Hester et al (2009), field methods in archaeology, 7^th ed, walnut creek California.

    Kothari, C.R (1990), Research Methodology: Methods and Techniques, 2^nd ed, Wile Eastern; New belh.

      Staeck, J.P (2002). Back of the Earth, An introduction to Archaeology. London, Mayfield publishing House Company.