+def relative_change_stdev(mean1, mean2, std1, std2):
+ """Compute relative standard deviation of change of two values.
+
+ The "1" values are the base for comparison.
+ Results are returned as percentage (and percentual points for stdev).
+ Linearized theory is used, so results are wrong for relatively large stdev.
+
+ :param mean1: Mean of the first number.
+ :param mean2: Mean of the second number.
+ :param std1: Standard deviation estimate of the first number.
+ :param std2: Standard deviation estimate of the second number.
+ :type mean1: float
+ :type mean2: float
+ :type std1: float
+ :type std2: float
+ :returns: Relative change and its stdev.
+ :rtype: float
+ """
+ mean1, mean2 = float(mean1), float(mean2)
+ quotient = mean2 / mean1
+ first = std1 / mean1
+ second = std2 / mean2
+ std = quotient * math.sqrt(first * first + second * second)
+ return (quotient - 1) * 100, std * 100
+
+