In a field study on jet lag, a condition created when the body's rhythm lags behind or ahead of the time of day it would be at the person's place of departure, the hypothesis was that the body's reactions of fatigue, dizziness, stomach aches, and mental confusion were caused by the rhythmic changes rather than just from the fatigue of flying. One group flew to China, crossing several time zones. Another group flew an equal amount of time and distance, but crossed NO time zones. In the study above, what was the independent variable?
a) The group that does not fly to Asia
b) The group that does not fly at all
c) Fatigue, trouble making decisions, dizziness, stomach aches
d) The alteration of the light-dark cycle from the time-changing flight path

In a field study on jet lag, where one group flew to China, crossing several time zones. Another group flew an equal amount of time and distance, but crossed no time zones, the independent variable is the alteration of the light-dark cycle from the time-changing flight path.

Explanation:

In a research study, the independent variable is one that can be manipulated to produce an effect on the dependent variable, effects that can be measured or quantified.

In the proposed case, the independent variable is alteration of the light-dark cycle from the time-changing flight path, since this determined which group travels through different time zones, and which group makes the flight without changing time zones. In the first group it can observe the appearance of Jet lag, and its symptoms, as a result of the time-changing flight path.

The other options are not correct, due to Ñ

    a) The group that does not fly to Asia  are the research subjects.

    b) The group that does not fly at all is not included in the study

    c) Fatigue, trouble making decisions, dizziness, stomach aches are effects of Jet lag, the dependent variable, whose appearance is the result produced by the independent variable.