Dr. Mindfog, is a drug researcher interested in investigating the mind-altering effects of two very potent drugs, scotch and tequila. Specifically, Dr. Mindfog wonders, "Is there a difference between the two drugs in their mind-altering effects?" Wishing to minimize and effects due to physical differences in groups of subjects, he selects ten adult twin pairs to participate in his study (five mail twin pairs and five female twin pairs, obviously matched). One member of each twin pair is randomly assigned to one of two groups, such that one member of a twin pair is in the "scotch" group and the other member of the twin pair is in the "tequila" group. Then, using the famous Olson Mind Dazedness Test (OMDT) he measures each participant's dazedness after self-administering three ounces of the drug within an hour's time. Below are the dazedness scores of Dr. Mindfog's experiment -- the higher the score, the more dazed the participant.

Twin Pairs	Group 1 Scotch Dazedness Scores	Group 2 Tequila Dazedness Scores
Bob & Bubba	7	9
Fred & Frank	4	4
Tim & Tom	6	5
Mary & Madeline	5	8
Elvira & Evelyn	4	3
Juan & Jaime	4	8
Charla & Carla	9	10
Jim & John	8	9
Cindy & Sandy	5	8
Margaret & Marlene	3	4

With = .05, determine the critical value of z* , t*, or r* that needs to be employed here. The value is: