1. Numeracy & Quantitative Methods Laura Lake

2. A census: - collecting information from each and every person of interest. A sample: - when the population is too large to undertake a census the a sample is needed - a sample is collecting information from only a part or subset of the total possible participants. A Census or a Sample?

3. A census every ten years since 1801. Count of all people and households in England and Wales with everyone asked the same questions on the same day to provide a snapshot of the population at one point in time. The statistics describe the population at national, regional and local levels. Carried out by the Office for National Statistics (ONS). Example of the UK Census

4. Population – the total number of units/ cases from which as sample will be taken. -It is not just about individuals, the population can be any unit e.g. companies, households, newspapers, websites. Target population – the whole group (units/cases) of interest about which the research wishes to draw conclusions. Example – in a study of heart attacks amongst men aged 50-60 years old the total population would be all men and the target population would be all men aged 50-60 years old. Sampling Terminology: Population

5. What is a sample? The portion (sub-set) of the population used for the research. Sampling frame – a list that includes every member of the population from which a sample is to be taken. Sampling units – the units/ cases selected for the research. Sampling Terminology: Frames & Units

6. Need to evaluate the effectiveness and efficiency of any sampling frame. Issues to consider with developing sampling frames: Is the frame comprehensive – all target population included? The full range of dimensions and information needed to inform the sample selection should be covered. Poor sampling frame can lead to under or over coverage – impact on findings, resources and costs of research. Sampling Terminology: Frames & Units

7. Other practical considerations: Can the frame easily identify those with the relevant characteristics? Are the potential respondent contact details are complete and up-to-date? Sampling Terminology: Frames & Units

8. Representative sample – a sample that accurately reflects the characteristics of the total population. -Larger samples are not necessarily better – how representative a sample it depends on the sampling technique used and the size of the population. Sampling bias – what can happen when all members of the population in the sampling frame do not have an equal chance of being selected. Sampling Terminology

9. Sampling variability – the different values which a given function of the data takes when it is computed for two or more samples drawn from the same population. Sampling error – errors in research results due to difference between the population and the sample used (when the sampling has not been representative). Sampling Terminology

10. Non sampling error – error in the research results due to problems with the sampling approach (e.g. non response). Non response – failure to obtain a measurement on one or more variables for one or more elements of the research. Sampling Terminology

11. Probability sample – a method of sampling that uses of random selection so that all units/ cases in the population have an equal probability of being chosen. Non-probability sample – does not involve random selection and methods are not based on the rationale of probability theory. Sampling Terminology: Types of Sampling

12. Bryman, A. (2008) Social Research Methods. 3 rd Ed. Oxford: Oxford University Press. David, M. and Sutton, C. (2004) Social Research :The Basics. London: Sage. ESRC Survey Measurement Programme. Online: available from Survey Resource Network http://www.surveynet.ac.uk/http://www.surveynet.ac.uk/ Oppenheim, A. (2000) Questionnaire Design, Interviewing and Attitude Measurement. London: Continuum References

13. This resource was created by the University of Plymouth, Learning from WOeRk project. This project is funded by HEFCE as part of the HEA/JISC OER release programme.Learning from WOeRk This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).http://creativecommons.org/licenses/by-nc-sa/2.0/uk/ The resource, where specified below, contains other 3 rd party materials under their own licenses. The licenses and attributions are outlined below: 1.The name of the University of Plymouth and its logos are unregistered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. 2.The JISC logo, the and the logo of the Higher Education Academy are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license. Author Laura Lake InstituteUniversity of Plymouth Title Numeracy & Quantitative Methods Sampling: Census, samples & sampling terminology Description Overview of key sampling terminology. Date Created March 2011. Educational Level Level 5 Keywords UKOER LFWOERK UOPCPDRM Learning from Woerk WBL Work Based Learning CPD Continuous Professional Development Census, sample, population, target population, sampling frame, sampling units, representative sample, sampling bias, sampling variability, sampling error, non response, non sampling error, probability and non probability sample. Creative Commons License Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license Back page originally developed by the OER phase 1 C-Change project ©University of Plymouth, 2010, some rights reserved