The results of the meta-analysis for the agronomic and phenotypic characteristics for Experimental Phase studies are presented in Fig. 2 (top), and the means and standard errors from individual analyses are presented in Table 1. Agronomic and phenotypic data were collected for 12 different variables across 15 Experimental Phase studies, except that ear height was analyzed in only 11 studies (Table 1). Data were analyzed individually and by meta-analysis to test for differences between the three GM maize hybrids and the conventional control for all variables except dropped ears, which had zero variability, preventing application of a statistical analysis. Thus, a total of 33 statistical tests were conducted between the three GM maize hybrids and the conventional control for 11 variables. No statistical differences were detected for early stand count, days-to-anthesis, days-to-silking, root lodging, stalk lodging, or final stand count for any of the GM hybrids compared to the conventional hybrid control (Table 1, Fig. 2). Furthermore, as noted above, no differences were observed for dropped ears between test and control entries as mean values were numerically low, with zero variability. Statistically significant differences (p ≤ 0.05) between MON-89Ø34-3 × MON-88Ø17-3 and the conventional hybrid control were found for ear height (108.2 vs. 103.3 cm), plant height (210.2 vs. 204.0 cm), grain moisture (18.8 % vs. 18.0 %), and grain yield (10.2 vs. 9.2 t ha−1). Statistically significant differences between MON-89Ø34-3 × MON-ØØ6Ø3-6 and the conventional hybrid control were detected for seedling vigor (7.6 vs. 6.6, on a scale of 1 = poor, 9 = best), plant height (208.2 vs. 201.7 cm), grain moisture (18.5 % vs. 18.1 %), and grain yield (10.0 vs. 9.1 t ha−1). The only statistically significant difference detected between MON-ØØ6Ø3-6 and the conventional control was seedling vigor (7.2 vs. 6.5). For MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6 GM maize hybrids, which expressed both insect control (IR) and HT traits, plant height, grain moisture, and grain yield were the three characteristics in common that showed significantly higher values than the conventional hybrid control.Fig. 2Agronomic and phenotypic combined study effect and confidence intervals of MON-89Ø34-3 × MON-88Ø17-3, MON-89Ø34-3 × MON-ØØ6Ø3-6, and MON-ØØ6Ø3-6 GM maize hybrids compared to the conventional control from Experimental Phase (top) and Pilot Phase (bottom) studies. Confidence intervals are shown as standardized differences (differences indicated in standard deviation units) derived from the meta-analysis. Asterisks indicate statistically significant differences between test and control at the 5 % level of significance Table 1Means and standard errors (SE) for phenotypic and agronomic characteristics of MON-89Ø34-3 × MON-88Ø17-3, MON-89Ø34-3 × MON-ØØ6Ø3-6, and MON-ØØ6Ø3-6 GM hybrids and the conventional control for Experimental Phase studies in Mexico during 2009–2013Characteristic (unit)Number of studiesExperimental Phase trialsMON-89Ø34-3 × MON-88Ø17-3MON-89Ø34-3 × MON-ØØ6Ø3-6MON-ØØ6Ø3-6Mean (SE)Mean (SE)Mean (SE)TestControlTestControlTestControlSeedling vigor (1 [poor] to 9 [best])157.0 (0.3)6.7 (0.2)7.6 (0.3)*6.6 (0.3)7.2 (0.2)*6.5 (0.2)Early stand count15199.4 (35.0)202.0 (36.0)194.8 (35.5)202.7 (36.0)200.6 (32.5)202.8 (36.0)Days-to-silking1580.6 (5.4)80.3 (5.3)81.0 (5.4)80.6 (5.3)79.9 (5.2)80.3 (5.3)Days-to-anthesis1578.9 (5.3)78.2 (5.1)78.6 (5.2)78.4 (5.1)77.9 (5.0)78.1 (5.0)Ear height (cm)11108.2 (7.5)*103.3 (7.4)106.9 (8.0)103.1 (7.4)103.9 (7.8)102.3 (7.6)Plant height (cm)15210.2 (6.6)*204.0 (6.5)208.2 (7.5)*201.7 (7.6)204.8 (7.4)202.7 (7.3)Final stand count15109.6 (12.6)103.3 (12.1)108.6 (13.4)102.8 (12.2)103.0 (11.5)103.0 (12.1)Root lodging (%)153.5 (1.7)2.7 (1.1)2.9 (1.1)2.1 (0.8)3.6 (2.0)2.3 (0.8)Stalk lodging (%)152.7 (1.1)4.1 (1.8)3.7 (2.1)4.0 (1.8)4.0 (1.7)4.0 (1.8)Dropped earsa 150.04 (0.03)0.08 (0.07)0.02 (0.02)0.12 (0.07)0.07 (0.05)0.08 (0.07)Grain moisture (%)1518.8 (1.0)*18.0 (0.9)18.5 (1.0)*18.1 (0.9)18.0 (1.0)18.1 (0.9)Grain yield (t ha−1)1510.2 (0.6)*9.2 (0.7)10.0 (0.6)*9.1 (0.8)9.1 (0.8)9.1 (0.8)* Statistically significant at the 5 % level of significance aData on dropped ears were collected but not included in the meta-analysis due to lack of variability