Depends how you plan to analyze the data whether you use long or wide formats. SPSS has a "wizard" to allow you to move between these, but it is not as user-friendly (at least for me) as some of SPSS's tools.

To efficiently enter data for each patient in SPSS for your longitudinal study, consider organizing your dataset in a wide format, where each patient is represented by a single row and each variable is recorded in multiple columns corresponding to different time points. This format allows you to easily enter data for each patient across time, maintaining a clear structure for analysis. Alternatively, you can use a long format where each patient has multiple rows, with one row for each observation at different time points. In this case, you would need to assign a unique identifier to each patient and use a variable to indicate the time point of each observation. Both wide and long formats have their advantages, so choose the one that best suits your research goals and analytical needs.

A database manager I worked with in the past would always go with the long file format--i.e., one row per time point with multiple rows per person. And that is my preference too. If some analysis you want to carry out requires a wide file format, you can use the CASESTOVARS command to restructure the data. See this UCLA tutorial:

• https://stats.oarc.ucla.edu/spss/modules/reshaping-data-long-to-wide-in-versions-11-and-up/

And for restructuring from WIDE to LONG:

• https://stats.oarc.ucla.edu/spss/modules/reshaping-data-wide-to-long-in-versions-11-and-up/

HTH.