Research internship project: preserve missing observations in a summary

Original invented practice inputs.

Task: A missingness profile with a documented analysis population.

Start with input.json and the CSV tables. Record your method before opening answer-key.json. Keep a changed input and explain how its result differs.

Technical reading:
https://pandas.pydata.org/docs/user_guide/missing_data.html

A result from this fixture is independent practice work; describe only work you actually complete.
