Table 2.

Descriptive statistics.

Variable name	Unweighted Mean (Standard deviation) (1)	Weighted (by the inverse of the number of estimates reported in each study) Mean (Standard deviation) (2)	Number of effect sizes (3)
Effect size (Cohen's d)	−0.112 (0.271)	−0.187 (0.436)	239
Effect size's standard error	0.021 (0.030)	0.035 (0.048)	239
Subject
Math/Science	0.423 (0.495)	0.401 (0.491)	101
Humanities	0.527 (0.500)	0.456 (0.499)	126
Mix	0.050 (0.219)	0.143 (0.351)	12
Level of Education
Primary	0.615 (0.488)	0.514 (0.501)	147
Secondary	0.343 (0.476)	0.359 (0.481)	82
Tertiary	0.042 (0.201)	0.127 (0.334)	10
Timing of student assessment during Covid-19
2020	0.657 (0.476)	0.676 (0.469)	157
2021	0.343 (0.476)	0.324 (0.469)	82
Geographical area
Europe	0.590 (0.493)	0.610 (0.489)	141
Non-Europe	0.410 (0.493)	0.390 (0.494)	98
Year of publication
2020	0.126 (0.332)	0.127 (0.334)	30
2021	0.702 (0.458)	0.644 (0.480)	168
2022	0.172 (0.378)	0.229 (0.421)	41
Type of data
Longitudinal	0.339 (0.474)	0.339 (0.474)	81
Cross-sectional	0.661 (0.474)	0.661 (0.474)	158
Type of research design
Descriptive	0.130 (0.337)	0.242 (0.429)	31
Correlational	0.765 (0.424)	0.555 (0.498)	183
Quasi experimental/experimental	0.105 (0.307)	0.203 (0.403)	25
Type of publication
Journal article	0.247 (0.432)	0.458 (0.499)	59
Other publication	0.753 (0.432)	0.542 (0.499)	180