Two independently operated laboratories provide historical dating services using radioactive carbon dating methods. A researcher suspects that one laboratory tends to provide older datings than the other laboratory. To investigate this supposition 18 samples of old material are split in half. One half is sent to laboratory A for dating, and the other half is sent to laboratory B for dating. The laboratories are asked to submit their answers to the nearest decade, and the results obtained are presented in DS 9.2.5. Is there any evidence that one laboratory tends to provide older datings than the other laboratory?