Ganssle and Lee discuss the probabilistic version of the problem of evil in their essay, “Evidential Problems of Evil.”  This argument is much more modest than the logical problem, as it does not argue that it is logically impossible that God should exist but that it is improbable in the face of evil and suffering.
Ganssle and Lee discuss a few versions of the problem, but the common thread among them is the move from the appearance that evil is unjustified to the conclusion that evil is unjustified. This may be done in an appeal to a particular and heinous act of evil or to evil generally. It seems as though the critic in this case attempts to position himself in such a way that the Christian must provide a sufficient justification for each and every instance of evil in order to defeat the argument.
This positioning of the critic is inappropriate. As Koukl explains in his book, Tactics, “The burden of proof is the responsibility someone has to defend or give evidence for his view.” In this case, it is the critic who is proposing a view (that God is unjustified in allowing evil). Therefore it is the critic who bears the burden of proving his view, not our responsibility to debunk it. In other words, the critic must show that it is improbable that God has justification to allow evil and not our responsibility to provide that justification.
Wykstra’s response is a good one.  He demonstrates that the move from the appearance to the probability is only appropriate when we are in a position to know. Wykstra demonstrates this by contrasting the determination that a hippopotamus is absent from a dog park with the determination that a dog whistle is not being blown in a dog park. Whereas one is in a position to see any hippos in attendance, one is not in a position to hear any dog whistle’s being blown.
William Lane Craig gives a similar response. He writes, “The burden of proof it lays on the atheist’s shoulders, namely, trying to show that the coexistence of God and suffering is impossible, is just too heavy to bear.”  Consider the following parallel arguments:
1) If God exists, then unjustified evil does not exist.
2) God exists.
3) Therefore, unjustified evil does not exist.
Compare this with:
1) If unjustified evil exists, then God does not exist.
2) Unjustified evil does exist.
3) Therefore, God does not exist.
The critical premises here will be premise two. One must choose what is more compelling, that God exists or that unjustified evil exists. There are independent reasons (such as the moral argument, cosmological argument, etc) to believe that God exists but there is no independent argument that unjustified evil exists. For these reasons, it seems more reasonable to believe that God does exist and therefore unjustified evil does not exist.
 Gregory E. Ganssle and Yena Lee, in God and Evil: The Case for God in a World Filled with Pain – Kindle Edition by Chad Meister and James K. Dew Jr. (Downers Grove: InterVarsity Press, 2013).
 Greg Koukl, Tactics: A Game Plan for Discussing Your Christian Convictions (Grand Rapids: Zondervan, 2009), 58.
 Ganssle and Lee, 2013.
 William Lane Craig, On Guard: Defending Your Faith with Reason and Precision – Kindle Edition (Wheaton: Good News Publishers, 2010).