ISO is totally fake
Still according to Tony Northrup Olympus and Fuji are the worst. They cheat about a full stop, so if you set the ISO at 400, you're shooting at about 200. It's an underexposure of 100%.
Why do all the manufactors do that? In that way it seems as a given camera is able to shoot noiseless at a higher ISO.
For me it's disgusting that the manufactors in this way bend the truth, and even more incompreehensive that the organisation ISO let them do it. So stick to the real ISO numbers or discard them and find another way to express the sensitivity of the sensor.
Click on the image to watch the video.