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An increasing number of researchers pool, harmonize, and analyze survey data from different survey providers for their research questions. They aim to study heterogeneity between groups over a long period or examine smaller subgroups; research questions that can be impossible to answer with a single survey. This combination or pooling of data is known as individual person data (IPD) meta-analysis in medicine and psychology; in sociology, it is understood as part of ex-post survey harmonization (Granda et al 2010). However, in medicine or psychology, most original studies focus on treatment or intervention effect and apply experimental research designs to come to causal conclusions. In contrast, many sociological or economic studies are nonexperimental. In comparison to experimental data, survey-based data is subject to complex sampling and nonresponse. Ignoring the complex sampling design can lead to biased population inferences not only in population means and shares but also in regression coefficients, widely used in the social sciences (DuMouchel and Duncan 1983 and Solon et al. 2013). To account for complex sampling schemes or non-ignorable unit nonresponse, survey-based data often comes with survey weights. But how to use survey weights after pooling different surveys? We will build upon the work done by DuMouchel and Duncan (1983) and Solon et al.(2013) for survey-weighted regression analysis with a single data set. Through Monte Carlo (MC) simulations, we will show that endogenous sampling and heterogeneity of effects models require survey weighting to receive approximately unbiased estimates …