Context: Functional Size Measurement (FSM) methods, like Function Points Analysis (FPA) or COSMIC, are well-established approaches to estimate software size. Several approximations of these methods have been recently proposed as they require less time/information to be applied, however their effectiveness for effort prediction is not known.

Objective: The effectiveness of approximated functional size measures for estimating the development effort is a key open question, since an approximate sizing approach may miss to capture factors affecting the effort. Therefore, we empirically investigated the use of approximate FPA and COSMIC sizing approaches, also compared with their standard versions, for effort estimation.

Method: We measured 25 industrial software projects realised by a single company by using FPA, COSMIC, two approximate sizing approaches proposed by IFPUG for FPA (i.e. High Level and Indicative FPA), and three approximate sizing approaches proposed by the COSMIC organisation for COSMIC (i.e. Average Functional Process, Fixed Size Classification, and Equal Size Band). Then we investigated the quality of the regression models built using the obtained measures to estimate the development effort.

Results: Models based on High Level FPA are effective, providing a prediction accuracy comparable to the one of the original FPA, while those based on the Indicative FPA method show poor estimation accuracy. Models based on COSMIC approximate sizing methods are also quite effective, in particular those based on the Equal Size Band approximation provided an accuracy similar to the one of standard COSMIC.

Conclusion: Project managers should be aware that predictions based on High Level FPA and standard FPA can be similar, making this approximation very interesting and effective, while Indicative FPA should be avoided. COSMIC approximations can also provide accurate effort estimates, nevertheless, the Fixed Size Classification and Equal Size Band approaches introduce subjectivity in the measurement.

背景：功能大小测量（FSM）方法（如功能点分析（FPA）或COSMIC）是公认的估算软件大小的方法。这些方法的几种近似方法最近被提出，因为它们需要较少的时间/信息来应用，然而，它们对工作量预测的有效性尚不清楚。

目的：近似的功能规模度量用于估计开发工作量的有效性是一个关键的开放性问题，因为近似的大小确定方法可能无法捕获影响工作量的因素。因此，我们根据经验研究了近似FPA和COSMIC大小调整方法的使用，并与标准版本进行了比较，以进行工作量估算。

方法：我们使用FPA，COSMIC，IFPUG针对FPA提出的两种近似规模确定方法（即高级和指示性FPA）和COSMIC组织针对COSMIC提出的三种近似规模确定方法，测量了单个公司实现的25个工业软件项目（即平均功能过程，固定大小分类和等大小带）。然后，我们调查了使用获得的测度建立的回归模型的质量，以估算开发工作量。

结果：基于高水平FPA的模型是有效的，其预测准确性可与原始FPA的模型相媲美，而基于指示性FPA方法的模型则显示出较差的估计准确性。基于COSMIC近似大小调整方法的模型也非常有效，特别是基于等大小带近似的模型提供的精度类似于标准COSMIC之一。

结论：项目经理应意识到，基于高级FPA和标准FPA的预测可能是相似的，因此这种近似非常有趣且有效，而应避免使用指示性FPA。COSMIC近似值还可以提供准确的工作量估算，但是，“固定尺寸分类”和“相等尺寸带”方法在测量中引入了主观性。