A stochastic process has the Markov property if the conditional probability distribution of future states of the process (conditional on both past and present states) depends only upon the present state, not on the sequence of events that preceded it. A process with this property is called a Markov process. The term strong Markov property is similar to the Markov property, except that the meaning of "present" is defined in terms of a random variable known as a stopping time. Both the terms "Markov property" and "strong Markov property" have been used in connection with a particular "memoryless" property of the exponential distribution.
The term Markov assumption is used to describe a model where the Markov property is assumed to hold, such as a hidden Markov model.
A Markov random field extends this property to two or more dimensions or to random variables defined for an interconnected network of items. An example of a model for such a field is the Ising model.
A discrete-time stochastic process satisfying the Markov property is known as a Markov chain.
A stochastic process has the Markov property if the conditional probability distribution of future states of the process (conditional on both past and present values) depends only upon the present state; that is, given the present, the future does not depend on the past. A process with this property is said to be Markovian or a Markov process. The most famous Markov process is a Markov chain. Brownian motion is another well-known Markov process.
Let be a probability space with a filtration , for some (totally ordered) index set ; and let be a measurable space. A -valued stochastic process adapted to the filtration is said to possess the Markov property if, for each and each with ,
In the case where is a discrete set with the discrete sigma algebra and , this can be reformulated as follows:
Alternatively, the Markov property can be formulated as follows.
for all and bounded and measurable.
Strong Markov property
Suppose that is a stochastic process on a probability space with natural filtration . For any , we can define the germ sigma algebra to be the intersection of all for . Then for any stopping time on , we can define
Then is said to have the strong Markov property if, for each stopping time , conditioned on the event , we have that for each , is independent of given .
The strong Markov property implies the ordinary Markov property, since by taking the stopping time , the ordinary Markov property can be deduced.
Assume that an urn contains two red balls and one green ball. One ball was drawn yesterday, one ball was drawn today, and the final ball will be drawn tomorrow. All of the draws are "without replacement".
Suppose you know that today's ball was red, but you have no information about yesterday's ball. The chance that tomorrow's ball will be red is 1/2. That's because the only two remaining outcomes for this random experiment are:
|Day||Outcome 1||Outcome 2|
On the other hand, if you know that both today and yesterday's balls were red, then you are guaranteed to get a green ball tomorrow.
This discrepancy shows that the probability distribution for tomorrow's color depends not only on the present value, but is also affected by information about the past. This stochastic process of observed colors doesn't have the Markov property. Using the same experiment above, if sampling "without replacement" is changed to sampling "with replacement," the process of observed colors will have the Markov property.
- Markov chain
- Markov blanket
- Markov decision process
- Causal Markov condition
- Markov model
- Chapman–Kolmogorov equation
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- Feller, W. (1971) Introduction to Probability Theory and Its Applications, Vol II (2nd edition),Wiley. ISBN 0-471-25709-5 (pages 9 and 20)
- Dodge, Y. (2003) The Oxford Dictionary of Statistical Terms OUP. ISBN 0-19-850994-4
- Durrett, Rick. Probability: Theory and Examples. Fourth Edition. Cambridge: Cambridge University Press, 2010.