Sampling Scientific Research Methods in Geography Montello & Sutton Ch 8 Summary

Overview Sampling Frames and Sampling Designs Implications of Sampling Frames and Designs Spatial Sampling From Continuous Fields Sample Size Review/Discussion

Introduction Sampling populationSampling is any way of selecting a subset from the entire set of entities of interest called a population sampleThis subset is called a sample

Sampling Frames & Designs How samples are obtained What that means for the design and interpretation of research Population Sampling Frame Sample

Hierarchy of Design Sampling Frame Sampling Design Non-probability Sampling Snowball Sampling Convenience Sampling Probability Sampling Simple Random Sampling Systematic Random Sampling Stratified Random Sampling Cluster Sampling Multi-stage Area Sampling

Implications of Sampling Frames & Designs RepresentativenessRepresentativeness is the degree to which the smaller set resembles a larger set GeneralizabilityGeneralizability refers to the question of what larger set can we validly draw conclusions about from the evidence of the smaller set?

Implications cont. Nonparticipation biasNonparticipation bias exists if nonparticipants are different from participants The sample can become less representative of the sampling frame Volunteer biasVolunteer bias exists when cases get into studies by selecting themselves – “self-selection bias” ▫Common in non-probability sampling designs

Spatial Sampling From Continuous Fields Organizing or breaking continuous space into discrete objects, perhaps very small and numerous objects, and sampling and measuring from these objects TransectsTransects are linear features and a common method of this QuadratsQuadrats are breaking continuous space into discrete polygonal features shaped like squares independent spatial samplingBoth are probability sampling and are examples of independent spatial sampling

Spatial Sampling cont. Non-independent spatial samplingNon-independent spatial sampling is focused on locations of greater change in the trend ▫sampling on the basis of a model of patterns or trends in the spatial distribution of their property of interest Spatial interpolationSpatial interpolation refers to making inferences back to the continuous field after sampling is completed

Sample Size How large should a sample be? Benefits vs. costsBenefits vs. costs Larger samples can be more representative BUT cost more money, time and effort Researchers don’t have unlimited resources Consider your research goal and traditions of your sub-discipline of geography Power analysis & precision analysisPower analysis & precision analysis are used to find how large of a sample size is needed to get statistically significant results Effect sizeEffect size is the size of the relationship expresses as a proportion of noise within the data

Review/Discussion Give examples of some samples in geography Distinguish between probability and non- probability sampling How can you minimize non-participation and volunteer biases’ negative effects on research? Discuss ideas about what sample size would be good for your own thesis, or what you anticipate it being