"a twofold decrease" is correct and can be used in written English.
You can use it to describe a situation where a decrease happens in two stages—for example, "Research shows that the number of people in poverty has decreased by a twofold decrease since the start of the program."
Simultaneously, the air electroconductivity experienced a twofold decrease (Figure 1c).
A twofold decrease of NGB amounts was observed in Hq retinas.
An equivalent amount of 111In chloride resulted in a twofold decrease from 100±5%5% to 46±4%4% only.
Application of a 2 V/cm direct current electric field resulted in approximately a twofold decrease in the cell elasticity and depleted intracellular ATP.
While the formation of biofilms decreased almost by threefolds in Sebox5 and 7, a twofold decrease was evident in Sebox6 (Fig. 2a, b).
Moreover, Lisse et al. (2005) reported a twofold decrease in the water sublimation rate from 1983 to 1994, suggesting that the rate of water sublimation in the past was higher than the present rate.
After oxidization, the PL intensity has a twofold decrease, and we attribute this to the reduction of effective light-emitting centers or interface state as the small-sized silicon skeleton is fully oxidized into SiO2.
Increased apoptosis and reduced α-SMA staining were observed with complete freeing of the tissues from the posts but not upon removal of the magnet, resulting in a twofold decrease in post stiffness.
FAM appeared to be more sensitive to guanine-induced quenching with three and four guanine bases resulting in greater than a twofold decrease in the quantum yield of the fluorophore compared to the no-overhang target.
The oxygenated water intrusions led to a twofold decrease of the concentrations of hydrogen sulphide, ammonia, phosphate and silicate in the deep layers with a simultaneous increase of these nutrients and a decrease of the pH level in the surface layers.
Based on the data, the inhibition rate of EC growth (59.41 ± 3.45%) in variant 1 was accompanied by a twofold decrease in the concentrations of CD44high cells in comparison with the control that was also reflected in the reduction of CD44high/CD117+ ratio (Table. 3).
