From an extensive literature review, a total of 16 success variables were identified. Before including them in the final draft of questionnaire, they were statistically validated using Content Validity Ratio (CVR). This internal validation was carried out by asking 40 experts (i.e. construction safety managers, safety engineers and senior safety officers who have been involved in managing safety in construction projects for at least 10 years) whether or not the defined 16 variables were "1 = essential", "2 = useful but not essential" or "3 = not necessary". Degrees of necessity were used as success variables for safety program implementation.