Attrition (343 KB)

Attrition (loss of sample) occurs when individuals initially included in a study are not included in the final study analysis. Attrition is a common issue in education research and can occur for many reasons. Download the Standards Brief to learn more about the causes of attrition and how the WWC assesses attrition for a study.

Baseline Equivalence (195 KB)

As part of the WWC review process for certain types of studies, reviewers assess whether the intervention group (those that received the intervention of interest) and the comparison group (those that did not receive the intervention) were similar at the start of the study. If these groups are similar, a study demonstrates baseline equivalence. Download the Standards Brief to learn more about how the WWC assesses baseline equivalence.

Confounding Factors (67 KB)

A confounding factor is an aspect of a study that makes it impossible to tell whether the intervention or that factor is responsible for differences in outcomes. In WWC study reviews, certified reviewers look for confounding factors that are always present for members of one group and never present for members of the other group. Download the Standards Brief to learn more about confounding factors and why studies with certain types of confounding factors cannot meet WWC design standards.