Moderator | Type | Number of effects | Number of articles | P value | Marginal R^{2} | Between-articles variance | ||

τ^{2} | I^{2} | Explained | ||||||

Without moderators | 644 | 101 | 2.8% | 42.9% | n.a. | |||

U-87 MG source | cat. | 644 | 101 | 0.075 | n.s. | 2.6% | ||

U-87 MG authentication | cat. | 644 | 101 | 0.476 | n.s. | 2.8% | ||

U-87 MG age (cell passages) | cont. | 138 | 11 | 0.238 | n.s. | 1.5% | ||

Cell concentration | cont. | 113 | 20 | 0.323 | n.s. | 3.8% | ||

Confluence level at cell passaging | cont. | 57 | 11 | 0.319 | n.s. | 0.8% | ||

Glucose level of culture medium | cat. | 644 | 101 | 0.016 | 7.0% | 2.5%* | 40.1% | 10.9% |

Mycoplasma exclusion | cat. | 644 | 101 | 0.491 | n.s. | 2.8% | ||

Supplemented antibiotics | cat. | 644 | 101 | 0.094 | n.s. | 2.6% | ||

FBS source | cat. | 644 | 101 | 0.067 | n.s. | 2.6% | ||

Type of untreated control | cat. | 644 | 101 | 0.370 | n.s. | 2.8% | ||

Articles reporting quality | int. | 644 | 101 | 0.031 | 3.3% | 2.6%† | 41.7% | 5.0% |

TMZ conc. | cont. | 644 | 101 | <0.001 | 38.6% | 3.4%‡ | 64.3% | 0.0% |

Treatment duration | cont. | 644 | 101 | <0.001 | 6.0% | 2.9%§ | 45.7% | 0.0% |

Random-effects three-level meta-regressions with the raw data the effects were calculated with as first level, the reported effects as second level and the articles the effects were reported in as third level. Marginal R

^{2}indicates the regression model fit69 ; τ^{2}: estimator of the variance of true effects; τ: square root of τ^{2}; I^{2}: proportion of between-articles variance of the total observed variance, including sampling error. τ^{2}estimator: restricted-maximum likelihood. The column ‘Explained’ indicates the reduction of τ^{2}after including the particular moderator compared with τ^{2}without moderators (only applicable if the number of included effects and articles is identical). For some continuous moderators, the number of effects and articles included in the regression is reduced due to non-reporting, which leads to a limited comparability of τ^{2}between parameters with different numbers of belonging articles and effects. ‘Not reported’ was included as a category for categorical moderators. P value is given for the test of the moderator. R^{2}, I^{2}and the explained heterogeneity were only calculated for moderators that prove significance in the test of the moderator (α=0.05).*95% CI of τ

^{2}: 1.7% to 3.6%.†95% CI of τ

^{2}: 1.8% to 3.8%.‡95% CI of τ

^{2}: 2.5% to 4.8%.§95% CI of τ

^{2}: 2.1% to 4.2%.cat., categorical; cont., continuous; FBS, fetal bovine serum; int., interval; n.a., not applicable; n.s., not significant; TMZ conc., temozolomide concentration; U-87 MG, Uppsala-87 Malignant Glioma.