Q: Is it duplicate submission if I write a paper using the data from an earlier published paper?
I am going to write a new paper reusing data from a paper which was submitted before. The purpose of the study is different between the two papers, but analysis methods are similar, accordingly the results are not so different. For novelty, a new analysis method is applied in the new paper. Is this practice regarded as duplicate submission or self plagiarism?
Usually publishing the result of the same dataset is considered as overlapping publication. Especially if the raw data, main study findings, and conclusion of both the publications are the same, the one published later might be regarded as duplicate publication. This publication practice is strongly discouraged by the ICMJE guidelines.
If however, you believe that although the second study uses the same data, the focus and purpose are significantly different from the previous study, you should clearly explain this citing the first study in the cover letter during submission. The first study should also be cited in the text of the manuscript and the fact that the second study was based on already published data should also be mentioned. You might also need to take permission from the journal where the first study was published.
This way, at least you can be transparent and your intentions will not be doubted. However, it will remain for the editor to decide whether such a publication is acceptable or not.