A researcher is trying to decide whether or not to add another variable to his regression model. He has estimated the following equation for the model from a sample of 28 observations. 
= 23.62 + 18.86x1 + 24.72x2
SSE = 1425
SSR = 1320
He has also estimated the model with an additional variable x3. The results are: 
= 25.32 + 15.29x1 + 7.63x2 + 12.72x3
SSE = 1350
SSR = 1465
What advice would you give this researcher? Use a .10 level of significance.
Definitions:
Transporting Molecules
The movement of molecules across cell membranes or within cellular compartments, essential for various biological processes.
Cell Membrane
The lipid bilayer surrounding a cell that controls the passage of substances in and out of the cell, maintaining the internal environment.
Concentration of Salts
The measure of the amount of dissolved salts in a solution, which can affect cellular processes and physiological functions.
Amount of Water
The amount of water refers to the quantity or volume of water present or required in a given context, crucial for life, health, and various processes.
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