A survey of 800 women shoppers found that 17% of them shop on impulse. What is the 98% confidence interval for the true proportion of women shoppers who shop on impulse

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Answer:

The 98% confidence interval for the true proportion of women shoppers who shop on impulse is  

              [tex]0.1391 < p < 0.2009[/tex]

Step-by-step explanation:

From the question we are  told that

     The  sample size is n = 800

      The sample  proportion is  [tex]\r p = 0.17[/tex]

 

Given that the confidence level is  98%  

The level of significance is evaluated as

      [tex]\alpha = 100 -98[/tex]

     [tex]\alpha = 2[/tex]%

      [tex]\alpha = 0.02[/tex]

given that this is a two tailed test

    [tex]\frac{\alpha }{2} = \frac{0.02}{2} = 0.01[/tex]

The critical values obtained from the normal distribution table is  

   [tex]z_{\frac{\alpha }{2} } = 2.33[/tex]  

Now the the margin of error is mathematically evaluated as

         [tex]MOE = 2.33 * \sqrt{\frac{0.17 (1-0.17)}{800} }[/tex]

          [tex]MOE = 0.0309[/tex]

the 98% confidence interval for the true proportion of women shoppers who shop on impulse is mathematically evaluated as

      [tex]0.17 - 0.0309 < p < 0.17 + 0.0309[/tex]

       [tex]0.1391 < p < 0.2009[/tex]

The 98% confidence interval for the true proportion of women shoppers will be:

"0.1391 < p < 0.2009".

Critical value and Margin of error

According to the question,

Sample size, n = 800

Sample proportion, [tex]\hat p[/tex] = 0.17

Confidence level = 98%

Now,

The level of significance will be;

→ α = 100 - 98

      = 2% or,

      = 0.02

Two-tailed be:

→ [tex]\frac{\alpha}{2}[/tex] = [tex]\frac{0.02}{2}[/tex]

     = 0.01

The critical value be:

[tex]z_{\frac{\alpha}{2} }[/tex] = 2.33

then, The margin of error be:

= 2.33 × [tex]\sqrt{\frac{0.17(1-0.17)}{800} }[/tex]

= 2.33 × [tex]\sqrt{\frac{0.17\times 0.83}{800} }[/tex]

= 2.33 × [tex]\sqrt{\frac{0.1411}{800} }[/tex]

= 0.0309

hence,

The 98% confidence level be:

= 0.17 - 0.0309 < p < 0.17 < 0.0309

= 0.1391 < p < 0.2009

Thus the above approach is correct.

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