Unité INSERM U669, Paris Sud Innovation Group in Adolescent Mental Health, Paris, France.
Int J Methods Psychiatr Res. 2011 Dec;20(4):235-49. doi: 10.1002/mpr.352. Epub 2011 Oct 24.
The ratio of subjects to variables (N/p), as a rule to calculate the sample size required in internal validity studies on measurement scales, has been recommended without any strict theoretical or empirical basis being provided. The purpose of the present study was to develop a tool to determine sample size for these studies in the field of psychiatry. First, a literature review was carried out to identify the distinctive features of psychiatric scales. Then, two simulation methods were developed to generate data according to: (1) the model for factor structure derived from the literature review and (2) a real dataset. This enabled the study of the quality of solutions obtained from principal component analysis or Exploratory Factor Analysis (EFA) on various sample sizes. Lastly, the influence of sample size on the precision of Cronbach's alpha coefficient was examined. The N/p ratio rule is not upheld by this study: short scales do not allow smaller sample size. As a rule of thumb, if one's aim is to reveal the factor structure, a minimum of 300 subjects is generally acceptable but should be increased when the number of factors within the scale is large, when EFA is used and when the number of items is small.
在内部有效性研究中，通常建议使用主题与变量的比例（N/p）来计算测量量表所需的样本量，但并没有提供任何严格的理论或经验依据。本研究的目的是开发一种工具，以确定精神病学领域这些研究的样本量。首先，进行了文献回顾，以确定精神科量表的特征。然后，开发了两种模拟方法来生成数据：（1）根据文献综述得出的因子结构模型，以及（2）实际数据集。这使得可以研究在各种样本量下从主成分分析或探索性因子分析（EFA）获得的解决方案的质量。最后，研究了样本量对 Cronbach's alpha 系数精度的影响。本研究不支持 N/p 比例规则：短量表不允许使用更小的样本量。一般来说，如果目的是揭示因子结构，则通常可以接受至少 300 个样本，但如果量表内的因子数量较多、使用 EFA 以及项目数量较少，则应增加样本量。
