Another reason why so many studies report the inefficacy of prayer is that it is impossible to eliminate the variables associated with the spiritual condition of those praying (is the petitioner even a believer?), the motivation for which they offer the prayer (is it to provide evidence or because the Holy Spirit has moved them to pray?), the way in which they offer their prayer (are they praying a formulaic expression or intentionally bringing requests to God?), and so on.
Ang isa pang dahilan kung bakit maraming pagaaral ang iniulat ang kawalan ng bisa ng panalangin ay imposibleng malaman ang espiritwal na kalagayan ng nananalangin (ang nananalangin ba ay talagang tunay na mananampalataya), ang motibo ng nananalangin (nananalangin ba sila para lamang magkaroon ng ebidensya? O ang Banal na Espiritu ang nagtulak sa isang tao upang manalangin?), ang paraan kung paano sila nananalangin (nananalangin ba sila na gamit ang isang pormula o intensyonal na humihiling sila sa Diyos?), at marami pang iba.