How Do You Maximize the Probability Interval for a Standard Normal Variable?

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SUMMARY

The discussion focuses on maximizing the probability interval for a standard normal variable Z, specifically finding the real number x that maximizes P(x < Z < x + α). The consensus is that setting x = 0 yields the largest spread, as indicated by the standard normal tables. To compute this, participants recommend using calculus to derive the expression P(x ≤ Z ≤ x + α) = Φ(x + α) - Φ(x) and finding its derivative to identify the maximum point.

PREREQUISITES
  • Understanding of standard normal distribution and the cumulative distribution function (CDF) Φ.
  • Basic calculus, including differentiation and finding critical points.
  • Familiarity with probability concepts and notation.
  • Knowledge of statistical tables for standard normal variables.
NEXT STEPS
  • Study the properties of the cumulative distribution function (CDF) for normal distributions.
  • Learn how to compute derivatives of functions involving the CDF.
  • Explore optimization techniques in calculus, specifically for functions with constraints.
  • Review advanced statistics topics, particularly those related to probability intervals and their applications.
USEFUL FOR

Students pursuing degrees in mathematics or statistics, educators preparing for advanced statistics courses, and anyone interested in understanding probability distributions and their applications in real-world scenarios.

Proggy99
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Homework Statement


Let Z be a standard normal random variable and \alpha be a given constant. Find the real number x that maximizes P(x < Z < x + \alpha)/


Homework Equations





The Attempt at a Solution


Looking at the standard normal tables, it seems obvious to me that x=0 gives the largest spread regardless of the value of the constant, but I am not sure how to find this computationally. Can anyone give me a hint on what direction to take? Thanks for any help.

I got most of the rest of the homework done, but the three I just posted really have me stumped.
 
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Proggy99 said:

Homework Statement


Let Z be a standard normal random variable and \alpha be a given constant. Find the real number x that maximizes P(x < Z < x + \alpha)/


Homework Equations





The Attempt at a Solution


Looking at the standard normal tables, it seems obvious to me that x=0 gives the largest spread regardless of the value of the constant, but I am not sure how to find this computationally. Can anyone give me a hint on what direction to take? Thanks for any help.

I got most of the rest of the homework done, but the three I just posted really have me stumped.

Looking at the level of your other posts, I'm assuming you have a calculus background? If not - sorry.
Note that

<br /> P(x \le X \le x + \alpha) = \Phi(x+\alpha) - \Phi(x)<br />

If this is maximized then its derivative (with respect to x) is zero. Find the derivative, and work with that.
 
statdad said:
Looking at the level of your other posts, I'm assuming you have a calculus background? If not - sorry.
Note that

<br /> P(x \le X \le x + \alpha) = \Phi(x+\alpha) - \Phi(x)<br />

If this is maximized then its derivative (with respect to x) is zero. Find the derivative, and work with that.

I took the calculus series as a freshman in college 19 years ago. I am struggling through a few higher level courses in my pursuit of a 7-12 integrated mathematics teaching degree. This homework is for an advanced statistics and probability class through independent study at LSU. I have abstract/modern algebra after this and I will have my math prereqs completed. I bought a calculus book to refresh my memory on some things while working through these classes. Number Theory is what brought me to these boards in the first place!

I am going to go see if I can figure it out from what you gave me. Thanks for the hint, I hope!
 

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