Half Width and Number of Replications

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# Half Width and Number of Replications - PowerPoint PPT Presentation

Half Width and Number of Replications. Prefer smaller confidence intervals — precision Notation: Confidence interval: Half-width =. Want this to be “small,” say &lt; h where h is pre-specified. Source: Systems Modeling Co. Half Width and Number of Replications (cont’d.).

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Presentation Transcript
Half Width and Number of Replications
• Prefer smaller confidence intervals — precision
• Notation:
• Confidence interval:
• Half-width =

Want this to be “small,” say

< h where h is pre-specified

Source: Systems Modeling Co.

Half Width and Number of Replications (cont’d.)
• Can’t control t or s
• Must increase n - how much?
• Set half-width = h, solve for
• Not really solved for n (t, s depend on n)
• Approximation:
• Replace t by z, corresponding normal critical value

Source: Systems Modeling Co.

Half Width and Number of Replications (cont’d.)
• Pretend that current s will hold for larger samples
• Get
• Easier but different approximation:

s = sample standard

deviation from “initial”

number n0 of replications

h0 = half width from “initial”

number n0 of replications

n grows quadratically as h decreases.

Source: Systems Modeling Co.