According to Chebysheff's Theorem,at least 93.75% of observations should fall within 4 standard deviations of the mean.

Chebysheff's theorem states that for any data set, regardless of distribution, at least 1 - 1/k^2 of the data will fall within k standard deviations of the mean. Therefore, for k = 2, at least 75% of observations will fall within 2 standard deviations of the mean, for k = 3, at least 88.89% of observations will fall within 3 standard deviations of the mean, and for k = 4, at least 93.75% of observations will fall within 4 standard deviations of the mean.