F-ratios of all behavioral measures for the main effects of ‘strain’ and ‘laboratory’ based on the GLM (split by experimental design): y = strain+laboratory+strain×laboratory; p≤0.001***, p≤0.01**, p≤0.05*, p>0.05 NS.

<p>F-ratios of all behavioral measures for the main effects of ‘strain’ and ‘laboratory’ based on the GLM (split by experimental design): y = strain+laboratory+strain×laboratory; p≤0.001***, p≤0.01**, p≤0.05*, p>0.05 NS.</p

Variation of strain main effects across the six laboratories in both designs.

<p>For each laboratory and experimental design, the main effect of ‘strain’ was separately calculated and displayed in terms of the mean F-ratio (+ s.e.m., square-root-transformed) across all 29 behavioral measures. Although the strain effect varied considerably among laboratories in the heterogenized design, the standardized design produced even more variable outcomes. Moreover, average F-ratios for ‘strain’ were considerably higher in the standardized design, indicating that treatment effects may be systematically overestimated by standardization.</p

Number of stretched postures on the elevated zero maze shown by C57BL/6NCrl and DBA/2NCrl mice.

<p>Data are presented as means (+ s.e.m., square-root-transformed, n = 16/strain and laboratory). The example illustrates large effects of the laboratory in the standardized (<b>A</b>) and heterogenized (<b>B</b>) design. Moreover, the direction of strain difference differed between Giessen and Munich in the standardized design.</p

Complete list of behavioral measures used for the analysis and the transformations applied to meet the assumptions of parametric analysis (NT = no transformation, log = log₁₀(y+1)-transformed, sqrt = square-root-transformed, angular = arcsin(square-root(y))-transformed).

<p>Complete list of behavioral measures used for the analysis and the transformations applied to meet the assumptions of parametric analysis (NT = no transformation, log = log₁₀(y+1)-transformed, sqrt = square-root-transformed, angular = arcsin(square-root(y))-transformed).</p

Between-experiment variation versus within-experiment variation.

<p>To assess the relative weight of between-laboratory variation versus within-laboratory variation, an F-ratio was calculated that reflects the partitioning of the ‘strain-by-block’ variance between all 24 blocks of one experimental design into variance due to variation between laboratories and variance due to variation within laboratories. For this, the mean squares of the ‘strain-by-laboratory’ interaction term were divided by the mean squares of the ‘strain-by-block’ interaction term. Data are displayed as mean F-ratios (+ s.e.m.; square-root-transformed) across all 29 behavioral measures for both conditions. F-ratios were significantly smaller in the heterogenized design (F_1,28 = 4.678, p = 0.039), demonstrating that heterogenization increased within-experiment variation relative to between-experiment variation.</p

Laboratory-specific testing procedures and apparatuses.

<p>Laboratory-specific testing procedures and apparatuses.</p

Variation between laboratories in the standardized and in the heterogenized design.

<p>The variation in strain differences is displayed as mean F-ratios (+ s.e.m.) of the ‘strain-by-laboratory’ interaction term calculated for 29 behavioral measures. F-ratios were determined separately for the two experimental designs, square-root-transformed to meet the assumptions of parametric analysis, and then compared using a GLM blocked by ‘behavioral measure’. F-ratios of the ‘strain-by-laboratory’ interaction terms were significantly lower in the heterogenized design (F_1,28 = 4.222, p = 0.049), indicating lower between-experiment variation.</p

Object exploration time in the novel object test shown by C57BL/6NCrl and DBA/2NCrl mice.

<p>Data are presented as means (+ s.e.m., square-root-transformed, n = 16/strain and laboratory). The example illustrates large effects of strain and laboratory in the standardized (<b>A</b>) and heterogenized (<b>B</b>) design. Moreover, the direction of strain difference differed between Giessen and Zürich in the heterogenized design.</p

Variation of mean strain differences in the standardized and heterogenized design across the six laboratories.

<p>Four examples of selected behavioral measures from four of the five behavioral tests are displayed: (<b>A</b>) Latency to fall off the pole in the vertical pole test, (<b>B</b>) number of open segment entries on the elevated zero maze, (<b>C</b>) number of corner entries in the open field test and (<b>D</b>) path travelled within the exploration zone in the novel object test. Strain differences varied considerably between laboratories in both designs, but were somewhat more consistent in the heterogenized design. Each laboratory tested 16 mice per strain for each experimental design.</p

Laboratory-specific housing conditions and animal care routines (STAN = standardized design, HET = heterogenized design).

<p>Laboratory-specific housing conditions and animal care routines (STAN = standardized design, HET = heterogenized design).</p