Answer:
observer bias
Explanation:
Based on the information provided within the question the thing that should concern us the most about Sandi's observations is Observer Bias. This term refers to the tendency of a researcher to see what they want as opposed to what is actually happening. This can be said because of Sandi's belief that McDonald clients are all overweight, by having this belief before actually having come to this conclusion with a series of tests, it might lead her to believe this to be true regardless of what she observes during the experiment.
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Air pressure is the wi get of air molecules pressing down on the earth. The pressure of the air molecules changes as you move upward from sea level into the atmosphere, the highest pressure is at sea level where the density of the air molecules is the greatest.