Calculate N for 95% Confidence in Iodine in Sea Water

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Discussion Overview

The discussion revolves around calculating the minimum number of samples (N) required to achieve 95% confidence in the mean value of iodine concentration in sea water, based on a given mean and standard deviation. The context is primarily statistical, focusing on confidence intervals and sample size determination.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a formula for calculating N based on the confidence interval and expresses confusion about their application of the t-value.
  • Another participant notes that the t-value is dependent on degrees of freedom, which in turn is influenced by N, raising a question about how to determine degrees of freedom from the provided information.
  • A further reply suggests that for an assumed N, calculating t is straightforward and proposes creating a table to relate confidence levels to N values to find an adequate sample size.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the calculation of the t-value and its dependence on N, indicating that there is no consensus on how to proceed with the problem.

Contextual Notes

There are limitations regarding the information provided, particularly the lack of clarity on how to derive degrees of freedom from the given data, which affects the calculation of the t-value.

Aerodynamic20
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Homework Statement



The determination of iodine in sea water gave a mean value of 46.43 μg/L and a sample standard deviation ss of 1.37 μg/L.

What is the minimum number of samples (N) which must be analyzed to have 95% confidence that the mean value differs from the true value by no more than 2.0%?

Homework Equations



u-x(bar)= +/- ts/rt(n) -------> n=(t^2)(s^2)/((u-x)^2)

The Attempt at a Solution



I know from the confident interval, the minimum at 95% is 1.96=t, s=1.37, e=0.02,
where am I going wrong?

Help please
 
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It's been awhile since I've done stats, but doesn't the t value depend on your degrees of freedom, which in turn depends on n?
 
Dopefish1337 said:
It's been awhile since I've done stats, but doesn't the t value depend on your degrees of freedom, which in turn depends on n?

It does but it is not given in the question. I don't know how possible it is to find the degree a freedom from the information given in the question. Any ideas folks?
 
For assumed N t is easy to calculate, isn't it? My stats are rusty as hell, but I think you can just prepare a table confidence vs N and check what N value is enough.

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methods
 

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