How to ensure that the digitizer is faulty? My HTC Evo 3D sometimes doesn't react when i press certain areas of the screen. I noticed it happens mostly on the part where the letter 'e' is, when i'm holding the phone in landscape mode.

So, i did a factory reset, wiped out SD card as well during the factory reset, and the problem still persists.

It sometimes happens for a certain period of time, and it starts to work after a while.

I did a line drawing test, and on some places it doesn't draw the line correctly (it is continuos but it's drawn with sharp angles, i don't know how to explain it better).

I read somewhere it is most probably a hardware problem, with a digitizer. Is there any way to be sure, or is it best to take it to a repair shop?
Open your settings menu and go all the way to the bottom, open Developer Options.

In the Input section, find the options called Pointer Location, and check it.

This is a feature for developers that shows the raw data from the digitizer.

Move your fingers around on the screen, and watch what you see, if your finger seems to disappear from the screen, Android is not seeing any data about it, it is a problem with your digitizer.