Surveys and censuses William Bredemeyer Methodology Presentation GEOG 5161: Research Design 5 March 2012

Overview Quantitative: Census Quantitative: Survey Qualitative ProsHuge sample size (100% sample); questions tested Question flexibility & affordability Discover new theory ConsFew questions; very expensive; undercount of some groups Larger samples expensive; validity and reliability can be poor Lack of generalization Best useTest theories where variables are included in the enumeration Test theories where extensive or new constructs needed Build brand new theories or gain deeper understanding Creswell 2009; Ellis 2009

Censuses Used to count the population (labor/soldiers/tax) Origins: early empires Modern censuses with several variables (1800s-present) Weeks 2008

Sampling strategyMethodPossible shortcoming Simple random samplePopulation sampled randomly Inefficient for rare strata Systematic sampleSet seed and sample every k th member of population Problematic if pattern in data Stratified sampleDivide population into strata and take certain sample from each group (used to oversample uncommon groups of pop.) Strata may not be known Cluster sampleDivide population into clusters and select sample from random set of clusters with cluster enumeration or one of the 3 other methods Homogeneity of clusters and cluster members can bias results Convenience sampleTake sample from easily accessed part of population only Risk of bias is high if generalizing to broader parts of population McGrew & Monroe 2000; Triola 2001

Biases in survey research: Some threats to validity Selection bias & non-response bias Loaded questions & order of items in a list Triola 2001; Freedman et al. 2007

Reliability When using multiple items to form a scaled score, check that they are consistent with tools such as Cronbach’s alpha. An alpha score closer to 1 indicates more correlation between items (0.7 or 0.8 is sufficient for most social science applications). Bland & Altman 1997

Geographic challenges with survey & census data analysis ChallengePotential solution Spatial autocorrelationSpatial regression Spatial nonstationarityGeographically weighted regression (GWR) Sample size effects hypothesis testsAdjust alpha-level or increase sample size; Bayesian approaches Underemphasis of the particularLocal statistical analysis (expansion method, GWR) Hierarchal data structureMultilevel modeling (if true hierarchy) Zolnik 2009

Applications of censuses and surveys in geography S/CApplicationAuthors CMeasure change in racial segregation and diversity in several US cities Holloway et al SStudy on commuting that uses some Netherlands census data (multilevel modeling) Schwanen et al S+Impacts of emigration from villages in Mexico to urban centers and the US (stratified sampling combined with some qualitative methods for ground truthing) Jones 2009 C+Population distribution across elevation & slope at several scales in NC (combine census and DEM) Patterson & Doyle 2011

References Bland, J Martin and Douglas G. Altman Statistics notes: Cronbach's alpha. BMJ 314: 572. Creswell, John W Research design: Qualitative, quantitative, and mixed methods approaches. 3 rd edition Sage: Los Angeles. Ellis, Mark Vital statistics. The Professional Geographer 61, no. 3: Freedman, David, Robert Pisani, and Roger Purves Statistics. 4 th edition. W. W. Norton & Company: New York. Holloway, Steven R., Richard Wright, and Mark Ellis The racially fragmented city? Neighborhood racial segregation and diversity jointly considered. The Professional Geographer 64, no. 1: Jones, Richard C Migration permanence and village decline in Zacatecas: When you can’t go home again. The Professional Geographer 61, no. 3: McGrew, J. Chapman, Jr., and Charles B. Monroe An introduction to statistical problem solving in geography. 2nd edition McGraw-Hill: Boston. Patterson, Lauren A. and Martin W. Doyle Hypsographic demography across scale. The Professional Geographer 63, no. 4: Schwanen, Tim, Frans M. Dieleman, and Martin Dijst The impact of metropolitan structure on commute behavior: A multilevel approach. Growth and Change 35, no. 3: Triola, Mario F Elementary statistics. 8 th edition Addison-Wesley: Boston. Weeks, John R Population: An introduction to concepts and issues. 4 th edition Thomson Wadsworth: Belmont, CA. Zolnik, Edmund J Context in human geography: A multilevel approach to study human-environment interactions. The Professional Geographer 61, no. 3: