Practical application of reference class forecasting for cost and time estimations: Identifying the properties of similarity

•Identify six key properties for project similarity based on in-depth interviews.•Determine reference class forecasting accuracy using inter- and intraaccuracy with cross validation.•Validate the performance of reference class forecasting based on empirical study of 52 real-life projects.•Accuracy depends on the number, combination and interaction effects of properties.•Trade-off exists between number of properties and size of the reference classes.