Athletes performing in bright sunlight often smear black eye grease under their eyes to reduce glare. Does eye grease work? In one study, 16 student subjects took a test of visual sensitivity to light‑and‑dark contrast after three hours facing into bright sun, both with and without eye grease. This is a matched pairs design. If eye grease is effective, subjects will be more sensitive to contrast when they use eye grease. The differences in sensitivity, with eye grease minus without eye grease, are provided in the table. Suppose that the subjects are an SRS of all young people with normal vision, that contrast differences follow a Normal distribution in this population, and that the standard deviation of differences is =0.22. What is the value of the test statistic? Give your answer to two decimal places.