Can clinical evaluation for a Class I SaMD app rely on literature from similar, but not equivalent, devices?

You can use data from equivalent devices for your clinical evaluation, but you are not required to do so. If you want to use literature on other devices, you need to describe how those devices are equivalent to yours, focusing on technical and clinical aspects (intended purpose, mode of action, target users, etc). For SaMD, biological equivalence is generally not relevant.

If you do not have clinical investigations or strictly equivalent devices, you should still demonstrate that your device performs as intended and that its benefits outweigh the risks. This can be done using a combination of literature, scientific rationale, and, if possible, post-market data or surveys. MDCG 2020-5 offers guidance on how to substantiate equivalence, but for Class I devices, the requirements are less stringent than for higher classes. The more closely the literature matches your app's features and intended use, the stronger your justification will be.

In summary, you can rely on published studies and data from similar devices, but you should clearly explain any differences and provide a scientific justification that your app is likely to perform as intended based on the available evidence.