Accidental clicks are clicks which occur by mistake or clumsiness. Accidental clicks must be taken into account when evaluating campaign performances, in particular for pay per click campaigns.
Accidental clicks affect desktop browsing but mostly mobile devices (smartphones and tablets) due to touch screens. Logically, smartphones are the most concerned because of small screen sizes. On mobile devices, accidental clicks are often called "fat fingers" clicks.
According to different studies, accidentals click are estimated from 20 to 40%. Unintentional clicks are usually detected and measured by observing post click behaviors. After a fat fingers clicks, users don’t stay on the landing page and don’t go further.
Some networks tend to filter accidental cliks, but it may be thought that most part of accidental clicks are still charged upon advertisers’ accounts.
Accidental cliks are only one part of invalid clicks.
Source: How Consumers Interact with Mobile App Ads (Pontiflex)
Source: Trademob study, 40% of mobile clicks are accidental or fraudulent 2012
"Fat fingers" clicks on mobiles devices according to GoldSpot Media 2012: