Potassium Levels in Spinach A study examining spinach leaves from a variety of different locations finds that spinach grown in soil with high amounts of iron tends to have lower levels of potassium. 1. Shea K. Health & Nutrition Update, Tufts University, August 11, 2019. How many variables are in this study? i How many of the variables are categorical? How many are quantitative? i eTextbook and Media Hint vvnicn is the explanatory variable? Amount of iron in soil Amount of potassium in spinach The different locations used in the study eTextbook and Media Hint Does the result appear to come from an observational study or an experiment? Observational Study Experiment eTextbook and Media Hint Can we assume that higher levels of iron in the soil cause spinach to have less potassium? Yes No eTextbook and Media Hint Are there likely to be any confounding variables in this study? Yes No