# Pooled data

When **pooled data** ( English *pooled data* from *to pool sth* ., Put together some) is called in the broadest sense records , data from several surveys together or studies. In a meta-analysis, this is done by combining primary investigations into metadata.

*Pooled data* is also used synonymously for panel data . On the other hand, *panel data is* also understood as a special case of *pooled data* , in the sense that although both dimensions (units of investigation and measurement times) are present, the units of investigation differ, e.g. B. Different people If different groups are interviewed alternately at recurring points in time, one speaks of a *rotating panel* .

In the context of longitudinal surveys or longitudinal studies , several *waves of* surveys can be combined. Panel data recorded the same key figures for different investigation units at different observation times. These could be investigated with linear panel data models ( *panel data models with fixed effects* ( English *fixed effects model* ) and *panel data models with random effects* ( English *random effects model* )). When *pooling* , one gives up a dimension and, for example, looks at all measured key figures in all years at the same time in order to examine a connection. One also speaks of *pooled cross section* . This increases the sample size . In addition, more precise estimators and test statistics can be obtained with higher test strength . However, the panel structure is lost and causal effects , for example, are more difficult to identify. In general, panel data are often considered to have advantages over pooled data, such as taking into account the heterogeneity of the units of investigation or fewer problems with autocorrelation and multicollinearity .

## Individual evidence

- ↑ Washington, SP, Karlaftis, MG, & Mannering, F. (2010). Statistical and econometric methods for transportation data analysis. Chapman and Hall / CRC. P. 161.
- ↑ Zaniolo, C., Ceri, S., Faloutsos, C., Snodgrass, RT, Subrahmanian, VS, & Zicari, R. (1997). Advanced database systems. Morgan merchant. P. 191.
- ^ Lewis, M. (2012). Applied statistics for economists. Routledge. P. 38.
- ↑ Häder, M. (2015). Empirical Social Research: An Introduction. Springer publishing house. P. 120.
- ^ Wooldridge, JM (2016). Introductory econometrics: A modern approach. Nelson Education. P. 8.
- ^ Wooldridge, JM (2016). Introductory econometrics: A modern approach. Nelson Education. P. 403.
- ↑ Mochimaru, M., Ueda, K., & Takenaka, T. (2014). Serviceology for services. In Selected papers of the 1st International Conference of Serviceology. Springer Japan. P. 166.