When I was looking for the accuracy values for the srtm dem, I found research papers trying to find out these values for its own selected area of study, some of them assume that the absolute value in Africa is around 5.6. I am new to studying remote sensing and GIS, so knowing where exactly to go for trusted information is a bit of challenge.
The absolute vertical accuracy of SRTM 1-arc second is equal or less than ± 16 meters ( at 90% confidence level).SRTM made use of a technique called radar interferometry in which two radar images are taken from slightly different locations. Differences between these images allow for the calculation of surface elevation or change. To get two radar images taken from different locations the SRTM hardware consisted of one radar antenna in the shuttle payload bay and a second radar antenna attached to the end of a mast extended 60 meters (195 feet) out from the shuttle.
The relative vertical accuracy is equal or less than ± 10 meters of SRTM 1-arc second.
(According to USGS)