Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Design and interpretation of studies: relevant concepts from the past
  and some extensions   Principles for the planning and analysis of observational studies, as
suggested by W.G Cochran in 1972, are discussed and compared to additional
methodological developments since then.

6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
20
The categories of this paper are: acc-phys
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
33
The categories of this paper are: plasm-ph
19
The categories of this paper are: eess