Q: Is it salami slicing if I publish two papers from two different data sets taken from the same participants?

Results based on the same dataset should be presented together in a single publication. Segmenting the results from the same data set into different manuscripts can amount to salami slicing or segmented publication. Please refer to the ICMJE guidelines regarding overlapping publication.

In your case, however, although the subject persons, time of data collection, and analytical methods are same, there are two different data sets that are independent of each other. Publishing two different articles based on the same dataset should not be a problem as long as the focus of the research question of each article is completely different.

For example, if you take data from the same set of patients about osteoporosis and brain tumor, it is possible to use these two independent sets of data for two different studies. However, it is crucial to be completely transparent in this matter, in your cover letter as well as both the manuscripts. So, for example,when writing the paper about the efficacy of a particular medicine on the treatment of brain tumor, you will have to mention that all these participants also had osteoporosis and mention whether the medicine had any effect on that condition. Likewise, the paper on osteoporosis should mention that all the participants had brain tumor as well. You should also cross-cite the methods section of the two papers because you used the same method for data collection and analysis. 

Additionally, it might be a good idea to discuss this with your supervisor or a senior colleague before arriving at a decision as there may be some field specific requirements that they would be aware of.

Related reading:

• Can I use data and methods from my previously published paper if I cite the source?
• Is it ethical to submit two papers using similar methods, but different materials and application?