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Conditioning on a third random variable may either increase or decrease the mutual information: that is, the difference <math>I(X;Y) - I(X;Y|Z)</math>, called the [[interaction information]], may be positive, negative, or zero. This is the case even when random variables are pairwise independent. Such is the case when: <math display="block">X \sim \mathrm{Bernoulli}(0.5), Z \sim \mathrm{Bernoulli}(0.5), \quad Y=\left\{\begin{array}{ll} X & \text{if }Z=0\\ 1-X & \text{if }Z=1 \end{array}\right.</math>in which case <math>X</math>, <math>Y</math> and <math>Z</math> are pairwise independent and in particular <math>I(X;Y)=0</math>, but <math>I(X;Y|Z)=1.</math>

Conditioning on a third random variable may either increase or decrease the mutual information: that is, the difference <math>I(X;Y) - I(X;Y|Z)</math>, called the [[interaction information]], may be positive, negative, or zero. This is the case even when random variables are pairwise independent. Such is the case when: <math display="block">X \sim \mathrm{Bernoulli}(0.5), Z \sim \mathrm{Bernoulli}(0.5), \quad Y=\left\{\begin{array}{ll} X & \text{if }Z=0\\ 1-X & \text{if }Z=1 \end{array}\right.</math>in which case <math>X</math>, <math>Y</math> and <math>Z</math> are pairwise independent and in particular <math>I(X;Y)=0</math>, but <math>I(X;Y|Z)=1.</math>

对于第三个随机变量条件的作用可能会导致增加或减少交互信息：其交互信息的差<math>I(X;Y) - I(X;Y|Z)</math>可以为正，负或零。即使随机变量是成对独立的也是如此。比如以下情况：

考虑到第三个随机变量条件可能会增加或减少'''<font color="#ff8000"> 互信息Mutual information </font>'''：例如其差值<math>I(X;Y) - I(X;Y|Z)</math>，称为'''<font color="#ff8000"> 交互信息Interaction information </font>'''(注意区分互信息Mutual information)，可以为正，负或零。即使随机变量是成对独立的也是如此。比如以下情况下：