Why are pre-post effect sizes should be avoided in meta-analyses?

Why are pre-post effect sizes should be avoided in meta-analyses?

Some meta-analyses, including several highly cited and influential ones, use the pre-post SMD, indicating the difference between baseline and post-test within one (treatment group). In this paper, we argue that these pre-post SMDs should be avoided in meta-analyses and we describe the arguments why pre-post SMDs can result in biased outcomes.

Do you use the pre or post SMD in a meta-analysis?

However, as indicated, some meta-analyses do not use this ‘regular’ type of SMD (the between-group SMD), but prefer to use the pre-post SMD, indicating the difference between the outcome score before the intervention (at pre-test) and the score after the intervention (at post-test).

Why are there large differences between pre-post SMDs?

Another corollary is that there are typically large differences between pre-post SMDs across studies, resulting in high levels of heterogeneity. Heterogeneity refers to the variability in the effect sizes that are found for included studies in a meta-analysis.

How is one group analysis used in a meta-analysis?

For this purpose, the single group of patients who were administered drug treatment will be taken into consideration. In matched group design, the unit of analysis is the pair of participants who have been matched on the basis of a particular attribute as deemed fit by the researcher.

Why are pre-post SMDs avoided in meta-analyses?

In this paper, we argue that these pre-post SMDs should be avoided in meta-analyses and we describe the arguments why pre-post SMDs can result in biased outcomes. One important reason why pre-post SMDs should be avoided is that the scores on baseline and post-test are not independent of each other.

Is the GET POST meta function case sensitive?

Please note that if a db collation is case insensitive (has with suffix _ci) then update_post_meta and delete_post_meta and get_posts () will update/delete/query the meta records with keys that are upper or lower case. However get_post_meta will apparently be case sensitive due to WordPress caching.

How big should the pre post effect size be?

In meta-analyses using pre-post SMDs, heterogeneity can be extremely high, sometimes more than 90% (Johnsen & Friborg, 2015 ).