@article{10902/29285,
year = {2010},
url = {https://hdl.handle.net/10902/29285},
abstract = {Meta-analysis of studies with two groups and two measurement occasions must employ order-one effect size indices to represent study outcomes. Especially with non-random assignment, non-equivalent control group designs, a statistical analysis restricted to post-treatment scores can lead to severely biased conclusions. The 109 primary studies included in 4 metaanalyses were recovered, and their authors were contacted to request the raw data to calculate the order-one effect size indices. From this total we only got 13 primary studies. The results with the raw data analysis were compared with those performed with the order-zero and order-one indices. Despite the difficulties for gathering the data, the few data sets analyzed show that if the meta-analysis is performed with order-zero indices, the results can be severely misleading},
publisher = {Universidad de Valencia},
publisher = {Psicológica: Revista de metodología y psicología experimental, 2010, 31, 291-315},
title = {The hard but necessary task of gathering order-one effect size indices in meta-analysis},
author = {Ortego Maté, María Carmen and Botella Asina, Juan},
}