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The pair { X , Y } has the joint distribution (in m-file npr08_06.m ):

X = [ - 2 . 3 - 0 . 7 1 . 1 3 . 9 5 . 1 ] Y = [ 1 . 3 2 . 5 4 . 1 5 . 3 ]
P = 0 . 0483 0 . 0357 0 . 0420 0 . 0399 0 . 0441 0 . 0437 0 . 0323 0 . 0380 0 . 0361 0 . 0399 0 . 0713 0 . 0527 0 . 0620 0 . 0609 0 . 0551 0 . 0667 0 . 0493 0 . 0580 0 . 0651 0 . 0589

Determine whether or not the pair { X , Y } is independent.

npr08_06 Data are in X, Y, P itestEnter matrix of joint probabilities P The pair {X,Y} is NOT independentTo see where the product rule fails, call for D disp(D)0 0 0 1 1 0 0 0 1 11 1 1 1 1 1 1 1 1 1
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The pair { X , Y } has the joint distribution (in m-file npr09_02.m ):

X = [ - 3 . 9 - 1 . 7 1 . 5 2 . 8 4 . 1 ] Y = [ - 2 1 2 . 6 5 . 1 ]
P = 0 . 0589 0 . 0342 0 . 0304 0 . 0456 0 . 0209 0 . 0961 0 . 0556 0 . 0498 0 . 0744 0 . 0341 0 . 0682 0 . 0398 0 . 0350 0 . 0528 0 . 0242 0 . 0868 0 . 0504 0 . 0448 0 . 0672 0 . 0308

Determine whether or not the pair { X , Y } is independent.

npr09_02 Data are in X, Y, P itestEnter matrix of joint probabilities P The pair {X,Y} is NOT independentTo see where the product rule fails, call for D disp(D)0 0 0 0 0 0 1 1 0 00 1 1 0 0 0 0 0 0 0
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The pair { X , Y } has the joint distribution (in m-file npr08_07.m ):

P ( X = t , Y = u )
t = -3.1 -0.5 1.2 2.4 3.7 4.9
u = 7.5 0.0090 0.0396 0.0594 0.0216 0.0440 0.0203
4.1 0.0495 0 0.1089 0.0528 0.0363 0.0231
-2.0 0.0405 0.1320 0.0891 0.0324 0.0297 0.0189
-3.8 0.0510 0.0484 0.0726 0.0132 0 0.0077

Determine whether or not the pair { X , Y } is independent.

npr08_07 Data are in X, Y, P itestEnter matrix of joint probabilities P The pair {X,Y} is NOT independentTo see where the product rule fails, call for D disp(D)1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1

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For the distributions in Exercises 4-10 below

  1. Determine whether or not the pair is independent.
  2. Use a discrete approximation and an independence test to verify results in part (a).

f X Y ( t , u ) = 1 / π on the circle with radius one, center at (0,0).

Not independent by the rectangle test.

tuappr Enter matrix [a b]of X-range endpoints [-1 1] Enter matrix [c d]of Y-range endpoints [-1 1] Enter number of X approximation points 100Enter number of Y approximation points 100 Enter expression for joint density (1/pi)*(t.^2 + u.^2<=1) Use array operations on X, Y, PX, PY, t, u, and Pitest Enter matrix of joint probabilities PThe pair {X,Y} is NOT independent To see where the product rule fails, call for D % Not practical-- too large
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f X Y ( t , u ) = 1 / 2 on the square with vertices at ( 1 , 0 ) , ( 2 , 1 ) , ( 1 , 2 ) , ( 0 , 1 ) (see Exercise 11 from "Problems on Random Vectors and Joint Distributions").

Not independent, by the rectangle test.

tuappr Enter matrix [a b]of X-range endpoints [0 2] Enter matrix [c d]of Y-range endpoints [0 2] Enter number of X approximation points 200Enter number of Y approximation points 200 Enter expression for joint density (1/2)*(u<=min(1+t,3-t)).* ... (u>=max(1-t,t-1)) Use array operations on X, Y, PX, PY, t, u, and Pitest Enter matrix of joint probabilities PThe pair {X,Y} is NOT independent To see where the product rule fails, call for D
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Source:  OpenStax, Applied probability. OpenStax CNX. Aug 31, 2009 Download for free at http://cnx.org/content/col10708/1.6
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