Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Accounting for Unobservable Heterogeneity in Cross Section Using Spatial
  First Differences   We develop a cross-sectional research design to identify causal effects in
the presence of unobservable heterogeneity without instruments. When units are
dense in physical space, it may be sufficient to regress the "spatial first
differences" (SFD) of the outcome on the treatment and omit all covariates. The
identifying assumptions of SFD are similar in mathematical structure and
plausibility to other quasi-experimental designs. We use SFD to obtain new
estimates for the effects of time-invariant geographic factors, soil and
climate, on long-run agricultural productivities --- relationships crucial for
economic decisions, such as land management and climate policy, but notoriously
confounded by unobservables.

23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph