The Role of Probability. Basic Concepts of Probability. A probability is a number that reflects the chance or likelihood that a particular event will occur. Probabilities can be expressed as proportions that range from 0 to 1, and they can also be expressed as percentages ranging from 0% to 100%.
Thus, when people hypoventilate (i.e. causing an increase in CO2) this causes the pH in your blood to decrease, making it more acidic. (and when hyperventilation occurs, O2 is increased, which causes an increase in pH - making blood more basic).
In other cases, the hypoventilation may be caused by another disease, or physical defect in the chest resulting in an abnormally shaped chest wall. People with muscular dystrophy run a higher risk of getting this disorder.