# Connecting the CDF and the PDF

Connecting the CDF and the PDF

The probability density function (PDF - upper plot) is the derivative of the cumulative density function (CDF - lower plot). This elegant relationship is illustrated here. The default plot of the PDF answers the question, "How much of the distribution of a random variable is found in the filled area; that is, how much probability mass is there between observation values equal to or more than 64 and equal to or fewer than 70?"

The CDF is more helpful. By reading the axis you can estimate the probability of a particular observation within that range: take the difference between 90.8%, the probability of values below 70, and 25.2%, the probability of values below 63, to get 65.6%.

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