V. Tangpricha et al. conducted a study to determine whether fortifying orange juice with vitamin D would increase serum 25-hydroxyvitamin D [25(OH)D] concentration in the blood. The researchers reported their findings in the paper "Fortification of Orange Juice with Vitamin D: A Novel Approach for Enhancing Vitamin D Nutritional Health" (American Journal of Clinical Nutrition, Vol. 77, pp. 1478-1483). A double-blind experiment was used in which 14 subjects drank 240 mL per day of orange juice fortified with 1000 IU of vitamin D and 12 subjects drank 240 mL per day of unfortified orange juice. Concentration levels were recorded at the beginning of the experiment and again at the end of 12 weeks. The following data, based on the results of the study, provide the before and after serum 25(OH)D concentrations in the blood, in nanomoles per liter (nmo/L), for the group that drank the fortified juice.
At the 1% significance level, do the data provide sufficient evidence to conclude that, on average, drinking fortified orange juice increases the serum 25(OH)D concentration in the blood?
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