With a 1 Ohm coil your voltage will be the square root of the wattage. That said, voltage is electronic and has nothing to do with anything.
For a study, the only reason they'd get a result is that a higher voltage produces a higher power.
Power levels determine the rate at which the mod transfers heat into the atomizer, and the maximum mass flow rate -- how much will be delivered to you.
The higher the power level, the more quickly the temperature will rise. You can burn your food whether you leave a burner on your stove at 5 or 10, but you need to watch it more at 10 as it gets hot more quickly.
For a study, the only reason they'd get a result is that, with everything else controlled, a higher power will produce a higher temperature. But really, if it's already up at an unsafe temperature, a lower power would still maintain it. So trying to correlate those two isn't really very thorough science in my opinion...
Temperature is the important factor for safety here. You can Google a bunch on thermal decomposition temperatures if you like. Stay at lower temperatures and you're golden.
In the low 4s, no vapor? Either your mod is inaccurate, your atomizer has very high losses, or it may take a while to get up to temperature: You will get no vapor production until the coil temperature is at least the boiling point of your liquid.