As a part of space research program, a physiologist was asked to investigate the effect of flight induced stress on blood pressure. Accordingly, the blood pressure of the cosmonauts were to be measured twice: once before the take-off and once after spacecraft entered the designated orbit around the earth. For a proper comparison, the preflight blood pressure should be recorded in:
|A||The lying down position|
|B||The sitting position|
|C||The standing position|
|D||Any position as long as the post-flight recording is made in the same position|
1. For two values to be comparable (to remove any bias) we must remove as many confounding variable possible "The confounding variable in this question is gravity.
2. Gravity is present on earth but is not present in space.
3. So, we have to take the BP in a position which sort of nullifies the effect of gravity on earth.
4. The best position is the lying down position because then the whole body is at the same height with respect to the heart.