Two commonly used techniques by which the lung volumes, TLC and RV

The following post has two assignments namely;

1.Two commonly used techniques by which the lung volumes, TLC and RV

Briefly describe two commonly used techniques by which the lung volumes, TLC and RV, can be measured, the principles underlying each method. In what clinical conditions are they likely to give differing results, and why?

2.Major problems used in secondary data sources, such as birth or death certificate data

What are the major problems used in secondary data sources, such as birth or death certificate data? What, if anything, can the evaluator do about these problems?