For evaluations of 2D target selection using Fitts' law, ISO 9241-411 recommends using the effective target width (W_e) calculated using the univariate standard deviation of selection coordinates. Related research proposed using a bivariate standard deviation; however, the proposal was only tested using a single speed-accuracy bias condition, thus the assessment was limited. We compared the univariate and bivariate techniques in a 2D Fitts' law experiment using three speed-accuracy biases and 346 crowdworkers. Calculating W_e using the univariate standard deviation yielded higher model correlations across all bias conditions and produced more stable throughput among the biases. The findings were also consistent in cases using randomly sampled subsets of the participant data. We recommend that future research should calculate W_e using the univariate standard deviation for fair performance evaluations. Also, we found trivial effects when using nominal or effective amplitude and using different perspectives of the task axis.

翻译：在基于费茨定律的二维目标选择评估中，ISO 9241-411推荐使用基于选择坐标单变量标准差计算的有效目标宽度（W_e）。相关研究曾提出使用双变量标准差进行计算，但该方案仅在单一速度-准确度偏差条件下进行过验证，评估存在局限性。本研究通过包含三种速度-准确度偏差条件、346名众包工作者参与的二维费茨定律实验，对比了单变量与双变量计算技术。结果表明：采用单变量标准差计算W_e能在所有偏差条件下获得更高的模型相关性，并在不同偏差间产生更稳定的吞吐量指标。在使用参与者数据随机抽样子集的情况下，该结论依然成立。我们建议未来研究应采用单变量标准差计算W_e以实现公平的性能评估。此外，研究发现使用名义振幅或有效振幅、以及采用不同任务轴向视角对结果仅产生微小影响。