## 3 Methodology
### Data Collection  
For the triangulation of information, the case studies were developed based on interviews and documentary analysis [37]. As the first data source, semi-structured interviews were conducted between July and September 2021. Due to the pandemic, it was not possible to conduct only on-site interviews; but using call-conference tools, the researchers were able to interview and visit the warehouses \"virtually\". The interviewees were logistics managers or logistics operations directors of the 3 PL providers, with a minimum working experience of five years in the industry at the middle to senior management level, as this ensures they have experienced the management of logistics services and closely followed the provision of these services over a period that spans across the typical duration of an outsourcing contract. This would provide a better level of understanding of the relevance of the warehouse features and their impact on the service quality performance. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Case Characteristics** & **Case 1** & **Case 2** & **Case 3** & **Case 4** & **Case 5** & **Case 6** & **Case 7** & **Case 8** \\ \hline \multirow{4}{*}{
\begin{tabular}{c} Number of employees \\ Turnover [EUR] \\ \end{tabular} } & \multirow{4}{*}{800} & \multirow{4}{*}{1000} & \multirow{4}{*}{150} & \multirow{4}{*}{1100} & \multirow{4}{*}{450} & \multirow{4}{*}{900} & \multirow{4}{*}{600} & \multirow{4}{*}{200} \\  & & & & & & & & & \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \cline{1-1} \cline{6-10}  & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Description of the case studies of 3 PL providers (data refers to the Italian market, and data on turnover refers to 2019). An interview guideline was developed for the semi-structured interviews with open and closed questions based on the literature review results (see Section 2). It facilitated data collection and ensured that interviews were conducted homogeneously [37]. Researchers asked interviewees to describe their viewpoint about the link between warehouse features and performance and rate, using the Kano model, the impact of the different features on the warehouse performance indicators. The researchers included in the interview guideline a questionnaire to record the rating score given by the interviewees. The performance indicators included in the analysis were derived from the literature review (Table 1) and previously validated by a panel of experts and tested with two 3 PL providers. Specifically, the panel of experts from the logistics and the real estate industry (i.e., one logistics manager with more than ten years of experience in the industry and one facility manager with more than 15 years of experience in the industry) helped to review the elements presented in Table 1, adding or modifying the wording. The result is shown in Table 4. Concerning Table 2, the panel of experts decide to maintain the warehouse features found in the literature. In addition, a pilot test of the interview guideline was carried out with a panel of academics (i.e., two academics with more than ten years of experience and publications in the logistics field of research) and two 3 PL providers (the same used for the text of the warehouse performance indicators and features). As a result, amendments were made to the wording of some questions to become more precise and focused. The pilot test assisted in avoiding misinterpretations [40], provided a solid interview guideline, and facilitated comparisons of the cases. Each interview (a total of eight interviews, one for each case) lasted between one hour and one hour and a half; the discussion was recorded and then transcribed within 24 h. The second source of data consisted of a documentary search.