Normal Distribution: Mean & Std Dev for Conditional Expected Values

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SUMMARY

A normal distribution is defined by its mean (μ) and standard deviation (σ). To calculate conditional expected values for a normal distribution, one can standardize the variable X using the z-statistic formula z = (x - μ) / σ. The expected value for a standard normal distribution restricted to X > 0 is calculated using the integral \(\frac{1}{\sqrt{\pi}}\int_0^\infty x e^{-x^2}dx = \frac{1}{2\sqrt{\pi}}\). For cases with non-zero mean or standard deviation not equal to 1, the integral becomes significantly more complex.

PREREQUISITES
  • Understanding of normal distribution parameters (mean and standard deviation)
  • Knowledge of z-statistics and standardization techniques
  • Familiarity with integral calculus and expected value calculations
  • Basic concepts of conditional probability in statistics
NEXT STEPS
  • Study the derivation of the expected value for truncated normal distributions
  • Learn about the properties of the standard normal distribution
  • Explore advanced integration techniques for complex integrals
  • Investigate applications of conditional expected values in statistical modeling
USEFUL FOR

Statisticians, data analysts, and students studying probability theory who are interested in understanding conditional expected values within normal distributions.

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A normal distribution can be completely defined by two parameters - the mean and the standard deviation. Given a normal distribution however, say X, how can I use just the mean and the standard deviation to give me conditional expected values for X<=0 and for X>0? I am guessing the distribution can be standardised to obtain a z-statistic.
 
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"Given a normal distribution however, say X" - I assume you mean that the variable [tex]X[/tex] has a normal distribution. Are both [tex]\mu[/tex] and [tex]\sigma[/tex] known?

"how can I use just the mean and the standard deviation to give me conditional expected values for [tex]X \le 0[/tex] and for [tex]X>0[/tex] ?"
This doesn't make sense to me as it stands. In statistics we take expected values of some function of a random variable - can you elaborate on what it is you seek?
 
If X has normal distribution with mean [itex]\mu[/itex] and standard deviation [itex]\sigma[/itex] then [itex]z= (x- \mu)/\sigma[/itex] has the standard normal distribution. As statdad said, "conditional expected values for X< 0 and X> 0" makes no sense." I might interpret as "suppose X a standard normal distribution, restricted to be larger than 0. What is the the expected value of X?"

That would be
[tex]\frac{1}{\sqrt{\pi}}\int_0^\infty x e^{-x^2}dx= \frac{1}{2\sqrt{\pi}}[/tex]
The general problem, with non-zero mean or standard deviation not 1 would be a much harder integral.
 
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