Given two established trends from national surveys conducted in 1983 and 2009: 1) Within any single year, as household income decreases, the average reported stress level increases. 2) Between 1983 and 2009, the average reported stress level rose for every income bracket. Based on these two trends alone, which of the following comparisons of stress levels is the most ambiguous and cannot be confidently made without knowing the specific magnitude of the changes?