The Quasi Biennial Oscillation, the downward propagating easterly and westerly wind regimes in the equatorial
stratosphere, has been investigated according to robust statistics that utilizes the amplitude/vector probable error ratio to
provide the confidence level of the investigated harmonic. The amplitude-to-noise ratio is found to be the highest in
correspondence of the 28- month harmonic for each examined height; the relative amplitude and phase values are found,
respectively, to decrease and increase with the height and to take about a year to descend from 15 to 70 hPa with a
progressive lag of about 1 month/km. At the top of the stratosphere, easterlies dominate, while at the bottom, westerlies
are more likely to be found.