In a metabolic study, four male swine were tested three times: when they weighed 30 kg, again

Question:

In a metabolic study, four male swine were tested three times: when they weighed 30 kg, again when they weighed 60 kg, and again when they weighed 90 kg. During each test, the experimenter analyzed feed intake and fecal and urinary output for 15 days, and from these data calculated the nitrogen balance, which is defined as the amount of nitrogen incorporated into body tissue per day. The results are shown in the accompanying table.25

Suppose these data are analyzed by linear regression. With X = body weight and Y = nitrogen balance, preliminary calculations yield = 60 and = 18.7. The slope is b1 = 0.017, with standard error SEb1 = 0.032. The t statistic is ts = 0.53, which is not significant at any reasonable significance level. According to this analysis, there is insufficient evidence to conclude that nitrogen balance depends on body weight under the conditions of this study.
The above analysis is flawed in two ways. What are they? (Look for ways in which the conditions for inference are not met. There may be several minor departures from the conditions, but you are asked to find two major ones. No calculation is required.)