It is found that at high pressures (above 100 mmHg) electron detachment is barely detectable or is absent, while at low pressures (below 100 mmHg) it is measurable. Thus the ionisation and attachment coefficients determined from the high-pressure experiments neglecting detachment appear to be still valid. This effect may account for the discrepancy between the data from (low-pressure) electron-avalanche studies and the (mainly high-pressure) steady-state experiments.