There are several meanings given to the word, evangelical, so it is a word that can be used for equivocation.  In a recent study, people who were evangelical by the definition below were more happy than those who were not evangelical.

Evangelical Of, relating to, or being a Christian church believing in the sole authority and inerrancy of the Bible, in salvation only through regeneration, and in a spiritually transformed personal life. 

The sole authority and inerrancy of the Bible: This is the only belief that makes any sense since, over thousands of years and with billions of tax dollars spent, no one has found a single error in the Bible.

salvation only through regeneration:  This is the revelation that we can be reconciled to God through the work the Jesus did on the cross.  This is the acceptance of the free gift of God.  This is the rejection of the concept that God doesn't exist or doesn't care or doesn't judge.  This is the rejection of the notion that somehow we can earn our way to reconcile ourselves back to God.  If you or any person will receive this free gift, God will forgive all of your faults and sins and set you free from your slavery to sin.  Whoever wishes to remain a slave of sin, remains a slave and will reap the reward of sin, which is death.

a spiritually transformed personal life:  This is what Jesus said: "Without me you can do nothing."  The Bible says that we were saved to good works.  Good works are part of salvation.  Before salvation, through the blood of Jesus Christ, we were unable to do any good works.  Now, because Christ lives within, He can do His good works through us, if we will allow it.  It is always He who does the work and not we, ourselves.  Also, the process of completion continues until we reach the measure of the fullness of Christ.  Eph 4.

These three points are the key to happiness and a transformed life.

An understanding of the inerrancy of Scripture will lead to other beliefs, though there are many evangelicals who profess to believe the Bible but yet rationalize away certain verses or even rationalize in additional information much as an evolutionist adds to scientific observation and filters out certain scientific observation.  For instance, from Scripture, we can know some things about the nature of the Godhead, but we must guard against rationalized or spiritualized speculations.  This is just one example.