This thesis seeks to understand how available harmonized population microdata shape our understanding of recent demographic change. Three distinct essays explore–explicitly and implicitly–applications of pooled census and survey data. Two essays assess the complementarity of census microdata and data from international survey programs in low- and middle-income countries (LMICs). The third essay leverages integrated United States (U.S.) census and American Community Survey data to document the evolution of a rare phenomenon over time. In parallel, I advance knowledge in three key areas of social demography: female educational attainment, household size and composition, and living arrangements among young adults. The three studies are unified by their reliance on harmonized census and survey data from IPUMS. The first essay, “Trends in Female Education in Low- and Middle-Income Countries: Coherence across Data Sources” examines the coherence of estimates of female educational attainment across three data sources: census samples from IPUMS International, Demographic and Health Surveys (DHS), and UNICEF Multiple Indicator Cluster Surveys (MICS). The study determines how trends vary across data sources and assesses the extent to which these data sources offer a consistent record of progress in education. The study also provides an empirical account of educational expansion among women aged 25–29 between 1960 and 2017 across 75 LMICs. Results contribute to a better understanding of the validity of a critical independent variable in social science research and provide practical information about the reliability of comparative investigations using three important data sources for demographic and development studies. The second essay, “Discrepancies in Household Size and Composition Between Census and DHS Data Across 22 Low- and Middle-Income Countries” also examines coherence across data sources. This study compares measures of household size across census samples from IPUMS International and DHS surveys and identifies the origins of inconsistencies. The analysis documents differences in average household size across data sources and investigates the characteristics of the households and individuals included in the samples that drive discrepancies. The discussion sheds light on differences in the design and implementation of censuses and DHS surveys that may create biases. The results provide important evidence for researchers using these sources to study a variety of demographic outcomes. The final essay “Non-family Living Arrangements Among Young Adults in the United States” documents trends in non-family living arrangements in the U.S. over time and identifies the individual characteristics associated with living in non-family households. The study leverages integrated U.S. census and American Community Survey data available from IPUMS USA for the period 1990 to 2019 and represents an application of pooled census and survey data to study a rare sociodemographic phenomenon. The results provide new knowledge on living arrangements among young adults and open avenues for future research in this area. The thesis combines methodological scrutiny with substantive inquiry to strengthen evidence on the reliability of comparative research and illustrate the analytic potential of pooled microdata, with important implications for data collection, analysis, and future research.