Brief Description: All questions that aren't "expert-level questions" be tagged as a nonexpert question. As a rule of thumb, the kind of question that a PhD student or higher would ask or encounter in a PhD-level class is an expert-level question. More detailed guidelines are provided below. These criteria were formalized in this meta post.

Detailed description:

Guidelines: An "expert" question should contain ONE OR MORE the following properties.

1. Deals with a formal economic or econometric model. This includes questions about mathematical or statistical techniques.
2. Questions about computational implementation.
3. The question includes a reference to a peer-reviewed journal or a high-quality working paper series.
4. The question is about a data standard or data codebook, provided a link to the data codebook or data reference guide is provided. This does NOT include questions about a particular event in a data set. Such questions must satisfy one of the previous three criteria to be considered.

Commentary

• The criteria defining an expert-level question is seen as a set of guidelines. This may be modified in the future if it is too inflexible. As a rule of thumb, I would suggest that if it is the kind of question that a PhD student or higher would ask or encounter in a PhD-level class, then it counts.
• A question can still be an expert question without having any mathematical rigor as long as it references a research paper (peer-reviewed journal or high-quality working paper). This acts as a way to signal quality of a question. Remember, signals must be costly to be credible!
• The set of criteria defining an expert-level question is fairly objective, which should help to resolve concerns about meta-tags.
• We should continue to strictly enforce the policy of closing off-topic questions, poorly crafted questions, and pure homework questions. We should also continue to invite experts, etc. I propose that we also institute a policy that every question that doesn't meet the standards of being considered an expert-level question MUST be tagged as nonexpert.

Examples of Expert Questions

The following illustrate questions that satisfy one or more of the above criteria:

• This first question is an example of an expert question because it is a question about an econometric technique, satisfying criterion (1). It doesn't specifically reference a particular paper, but deals with a specific econometric technique. Bartik Instrument Intuition
• This is also an expert question under criterion (1). It doesn't include a reference to a specific peer-reviewed paper, but it is a question that mathematically describes an economic model. Optimal consumption in Merton-like portfolio choice model with constant wage
• This question satisfies (1) because deals with a mathematical technique. It doesn't include questions and doesn't outline a specific model. However, it does reference a mathematical concept. For this reason, it's an expert question. Note that it does include a reference to a textbook, but this book is NOT a peer-reviewed journal article as required by criterion (3). Intuition of the Kolmogorov Equations
• This question is an expert question because it concerns the computational implementation of an econometric model. It provides some example code and a description of what they are trying to accomplish. This qualifies under (2). Extract residuals from Uhlig's rejection method - Lag selection
• This question somewhat broad and does not include equations or a specific model. It's a somewhat "chatty" question. However, it does reference a specific result from a peer-reviewed paper. Admittedly, it could be improved by providing a reference to the specific paper---but it DOES include a link to the Wikipedia page about the specific set of papers.. This is an expert question under (3). The Sonnenschein-Mantel-Debreu results, what are the implications for macroeconomics?
• This question doesn't pertain to a specific model nor does it include a reference to a peer-reviewed journal article. However, the question regards interpreting a commonly used data set/data standard and it does includes a reference to the data guidebook. This qualifies as an expert question under (4). What's the difference (if any) between "fixed assets" and "fixed capital" in the UN SNA?

Acknowledgment: This proposal was formulated in conjunction with @1muflon1. It is a slight modification of the other proposal about the "beginner" tag.