In planning a study of the birth weights of babies whose mothers did not see a doctor while pregnant, a researcher writes the hypotheses as H0: x̄ = 2250 grams versus H1: x̄ < 2250 grams. What is wrong with this?
Why is it only a one-tailed hypothesis? Is the researcher not interested in larger babies?
If interested:
H1: mean ≠ 2250
The researcher's hypotheses are incorrectly written. The null hypothesis (H0) states that there is no significant difference between the sample mean (x̄) and a specified value, in this case, 2250 grams. However, the alternative hypothesis (H1) should reflect the researcher's expectation or the alternative scenario they are trying to prove, rather than just stating the direction of the difference.
In this case, since the researcher wants to investigate whether the average birth weight is lower than 2250 grams for babies whose mothers did not see a doctor while pregnant, the correct alternative hypothesis would be H1: x̄ < 2250 grams. This alternative hypothesis indicates the specific direction of the expected difference in the sample mean.