What is the percentage of game won in alternating penalties format for team going first?

Question

What is the percentage of game won in current format of alternating penalties for team going first in top European football competitions?

Main reason for asking this question is ABBA system for penalty shootout. Which was recently used in FA Community Shield match between Chelsea and Arsenal. In this system, the order of penalties would see the the team going first in the shootout taking one spot-kick before their opponents take two in succession. (Trial system for penalties)

The reason for this new system is, to reduce the potential advantage that the team taking a first penalty in a shootout have. IFAB says that the experiment follows growing evidence that the current penalty shoot-out system, as laid down in the Laws of the Game to determine the outcome of a match, gives an unfair advantage to the team taking the first penalty in each pair of spot kicks.

Study of Mr. Ignacio Palacios-Huerta, Professor, London School of Economics, shows that new ABBA format cuts down advantage to 54%. While many articles claim that, in current format of alternating penalties team going first wins 60% of time. And answer to this question will help to find out if the reason for this change is justified or not.

Answer 1

About 60%

As you mention, the starting team wins about 60% percent of the time.

This paper in the American Economic Review, freely available from the London School of Economics repository here, analyses every penalty shootout in a major tournament (world cup, continent cup, English/German/Spanish cup, uefa league and champions league) for which data was available, which roughly amounts to every shootout in a final ever, and in every round from around the year 2000. The data ends at 2008 as this is not a very recent paper.

The authors conclude that indeed there is a psychological advantage in going first, as the increased odds persist even when controlling for other variables, such as team strength and possible home advantage.

Although the authors of the paper feel confident rejecting the null hypothesis of going first giving no advantage, it is still possible that the true probability for the first team to win is some other value >50%, and the 60% found is simply an expression of variance.