This function calculates the Cronbach's alpha by quantitative answers of a questionnaire. The questionnaire's answers have to be a 2-dimensional matrix, which is the only function's input. If the result is greater than 0.8 then the answers are considered reliable. If the score is below 0.2 then the answers are not reliable at all. Note that a negative score (which may occur for statistical reasons) indicates that the answers are completely random.