Algorithms have been developed to systematically determine the skeleton of the underlying graph and, then, orient all arrows whose directionality is dictated by the conditional independencies observed.Alternative methods of structure learning search through the many possible causal structures among the variables, and remove ones which are strongly incompatible with the observed correlations. In general this leaves a set of possible causal relations, which should then be tested by analyzing time series data or, preferably, designing appropriately controlled experiments. In contrast with Bayesian Networks, path analysis (and its generalization, structural equation modeling), serve better to estimate a known causal effect or to test a causal model than to generate causal hypotheses. For nonexperimental data, causal direction can often be inferred if information about time is available. This is because (according to many, though not all, theories) causes must precede their effects temporally. This can be determined by statistical time series models, for instance, or with a statistical test based on the idea of Granger causality, or by direct experimental manipulation. The use of temporal data can permit statistical tests of a pre-existing theory of causal direction. For instance, our degree of confidence in the direction and nature of causality is much greater when supported by cross-correlations, ARIMA models, or cross-spectral analysis using vector time series data than by cross-sectional data. Derivation theories
Nobel laureate Herbert A. Simon and philosopher Nicholas Rescher claim that the asymmetry of the causal relation is unrelated to the asymmetry of any mode of implication that contraposes.
Plague or The Plague may refer to:

Agriculture, fauna, and medicine
Plague (disease), a disease caused by Yersinia pestis
An epidemic of infectious disease (medical or agricultural)
A pandemic caused by such a disease
A swarm of pest insects such as locusts
A massive attack of other pests afflicting agriculture
Overpopulation in wild animals afflicting the environment and/or agriculture
Plague, collective noun for common grackles

Historical plagues
List of epidemics
Antonine Plague, an ancient pandemic in 165–189 CE brought to the Roman Empire by troops returning from campaigns in the Near East
Black Death, the Eurasian pandemic beginning in the 14th century
Great Northern War plague outbreak, a European outbreak in the early 18th century
Great Plague of London, a massive outbreak in England that killed an estimated 20% of Londons population in 1665–1666
Plague of Athens, a devastating epidemic which hit Athens in ancient Greece in 430 BCE
Plague of Justinian, a pandemic in 541–542 CE in the Byzantine Empire
Plague Riot, a riot in Moscow in 1771 caused by an outbreak of bubonic plague

Modern plagues
Third plague pandemic or Third Plague, a major plague pandemic that began in China in 1855 until 1960
Manchurian plague (1910–11): Part of the third plague pandemic
HIV/AIDS, originally referred to as the "gay plague" when it was discovered in the 1980s (see History of HIV/AIDS)

Art, media, and entertainment
Art
Plague (painting), by Arnold Böcklin

Fictional entities
Plague, Lisbeth Salanders hacker friend and colleague in the Hacker Republic, e.g., see The Girl who Kicked the Hornets Nest#Trial
The Plague (G.I. Joe), a Cobra special forces team in the comic book G.I.