Question

In the Spacelab Life Sciences 2 payload, 14 male rats were sent to space. Upon their returns, the red blood cell mass (in milliliters) of the rats was determined. A control group of 14 male rats was held under the same conditions (except for space flight) as the space rats, and their red blood cell mass was also determined when the space rats returned. Is there evidence to suggest that the flight animals have a different red blood cell mass from the control animals?

Flight	Control
8.59	8.65
8.64	6.99
7.43	8.40
7.21	9.66
6.39	7.14
6.87	7.62
7.89	7.44
9.79	8.55
6.85	8.70
7.54	9.14
7.00	7.33
8.80	8.58
9.30	9.88
8.03	9.94

Answer 1

Difference Scores Calculations

Treatment 1

N₁: 14
df₁ = N - 1 = 14 - 1 = 13
M₁: 7.88
SS₁: 13.46
s²₁ = SS₁/(N - 1) = 13.46/(14-1) = 1.04


Treatment 2

N₂: 14
df₂ = N - 1 = 14 - 1 = 13
M₂: 8.43
SS₂: 13.14
s²₂ = SS₂/(N - 1) = 13.14/(14-1) = 1.01


T-value Calculation

s²_p = ((df₁/(df₁ + df₂)) * s²₁) + ((df₂/(df₂ + df₂)) * s²₂) = ((13/26) * 1.04) + ((13/26) * 1.01) = 1.02

s²_M1 = s²_p/N₁ = 1.02/14 = 0.07
s²_M2 = s²_p/N₂ = 1.02/14 = 0.07

t = (M₁ - M₂)/√(s²_M1 + s²_M2) = -0.55/√0.15 = -1.44

The t-value is -1.43678. The p-value is .162705

p > alpha

No difference