# Glossary

## Basic and useful concepts for the reading of this website

Bayesian theory calls for the use of the posterior predictive distribution to do predictive inference, i.e., to predict the distribution of a new, unobserved data point. That is, instead of a fixed point as a prediction, a distribution over possible points is returned. In the Bayesian view, a probability is assigned to a hypothesis.

Complex systems are networks made of a number of components that interact with each other, typically in a nonlinear fashion. Complex systems may arise and evolve through self-organization, such that they are neither completely regular nor com- pletely random, permitting the development of emergent behavior at macroscopic scales.

Deterministic model is a mathematical representation of a system in which relationships are fixed (i.e. no parameters characterized by probability distribution), so for fixed starting values it will always produce the same result.

Differentiation is the process of finding the derivative of a curve. And the word “derivative” is just the fancy calculus term for the curve’s slope or steepness. And because the slope of a curve is equivalent to a simple rate (like miles per hour or profit per item), the derivative is a rate as well as a slope.

Emergence (of complex systems) is a nontrivial relationship between the properties of a system at different scales (microscopic and macroscopic) over scale. Macroscopic properties are called emergent when it is hard to explain them simply from microscopic properties.

Enzootic refers  to  an  infectious  disease  that  is present in a host population at all times, but having low incidence within the population.

Epizootic refers  to  an  infectious  disease  outbreak in  a  population  that  affects  a  large  number  of animals simultaneously but does not persist.

Frequentist inference is a type of statistical inference that draws conclusions from sample data by emphasizing the frequency or proportion of the data.In the frequentist view, a hypothesis is tested without being assigned a probability.

The Goodness of fit of a statistical model describes how well your description of the world fits a set of observations. Measures of goodness of fit typically summarize the discrepancy between observed values and the values expected under the model in question.

Hypotheses (plural is important) – descriptions of how the world might work; they can often be translated into quantitative predictions via models. A hypothesis is an unproved theory, proposition, supposition, etc., tentatively accepted to explain certain facts or to provide a basis for further investigation.

An infectious  disease refers  to  the  change  in  the state  of  health  of  a  host  organism  as  a  result  of invasion  of  the  body  by  pathogenic  organisms. Note  that  the  disease  is  the  manifestation  of  theinfection in a host organism, but infection can occurwithout  causing  disease.

Model is a simplified representation of a system. It can be conceptual, verbal, diagrammatic, physical, or formal (mathematical).

Mechanistic models assume that a complex system can be understood by examining the functioning of each of its parts and how they are coupled together. Mechanistic models usually have a tangible, physical appearance, as the components of the system are real, solid and visible.

Parameter vs. Variable: The first is a fixed number, the second changing in time.

A parasite is an organism that lives in (endoparasites) or on (ectoparasites) the living tissue of a host organism;  the  biological  interaction  between  host and  parasite  is  called  parasitism.  Microparasites, which   include   viruses   and   bacteria,   reproduce within  their  hosts.  Macroparasites,  which  include multicellular   endo-   and   ectoparasites,   generally spend some portion of the life cycle away from the primary host.

A pathogen is any disease-producing microorganism or material (e.g prions are infectious proteins, but are not technically organisms).

A reservoir   host is   an   animal   species   that maintains a parasite life cycle and functions as the source of the infection for humans or other species.

Self-organization (of complex systems) is a dynamical process by which a system spontaneously forms nontrivial macroscopic structures and/or behaviors (order) over time.

Stochastic model has some of the parameters uncertain and these are thus characterized by probability distribution. For fixed starting values they will produce many different results depending on the actual values the random variable takes. The random variation is usually based on fluctuations observed in historical data for a selected period using standard time series techniques.

Vectorial  capacity  is  a  term  that  takes  into  account the  efficiency  of  the  vector  in  transmitting  the pathogen,  the  lifespan  of  the  infectious  hosts,  andthe  degree  of  contact  between  the  host  and  vector.

Theory is a systematic statement of principles involved, or a formulation of apparent relationships or underlying principles of certain observed phenomena which has been verified to some degree.

A zoonosis is  an  infection  or  disease  that  can  be shared between humans and wildlife.