Integrated backscatter (IB) has been used for ultrasonic tissue characterization. To assess the potential variables in IB measurements, we performed both theoretical simulations and in vitro phantom measurements. First, we simulated data in which the scatterer position randomly was varied. IB values for the resulting images were calculated. Second, RF data from a tissue-mimicking phantom were acquired. Third, an adapted imaging approach, based on phase insensitivity, was evaluated. For both the simulations and phantom measurements, IB showed a standard deviation of +/-20%. These large deviations can be explained by variations in interference of signals and are not related to the state of the tissue. Small deviations in position of the scatterers resulted in important variations in IB. They must be taken into account and may limit the use of IB in cardiological applications. An improvement potentially can be obtained using phase insensitivity in new ultrasound processing schemes.