Step 1 :First, we calculate the sample proportions of employees who skip breakfast before and after the free breakfast was offered. The sample proportion before the free breakfast was offered is given by \(\hat{p}_{1} = \frac{x_{1}}{n_{1}}\) where \(x_{1}\) is the number of employees who skip breakfast before and \(n_{1}\) is the total number of employees surveyed before. Similarly, the sample proportion after the free breakfast was offered is given by \(\hat{p}_{2} = \frac{x_{2}}{n_{2}}\) where \(x_{2}\) is the number of employees who skip breakfast after and \(n_{2}\) is the total number of employees surveyed after.
Step 2 :Given that \(x_{1} = 34\), \(x_{2} = 14\), \(n_{1} = 57\), and \(n_{2} = 28\), we find that \(\hat{p}_{1} = 0.5965\) and \(\hat{p}_{2} = 0.5000\).
Step 3 :Next, we calculate the standard error of the difference in proportions. The standard error is given by \(\sqrt{\frac{\hat{p}_{1}(1-\hat{p}_{1})}{n_{1}} + \frac{\hat{p}_{2}(1-\hat{p}_{2})}{n_{2}}}\). Substituting the values we have, we find that the standard error is approximately 0.1147.
Step 4 :Finally, we calculate the 90% confidence interval for the difference in proportions. The confidence interval is given by \((\hat{p}_{1} - \hat{p}_{2}) \pm z \times SE\) where \(z\) is the z-score for a 90% confidence interval and \(SE\) is the standard error. Given that \(z = 1.645\), we find that the 90% confidence interval for the difference in proportions is approximately (-0.0921, 0.2851).
Step 5 :This means that we are 90% confident that the true difference in proportions of employees who skip breakfast before and after the free breakfast was offered is between -0.0921 and 0.2851.
Step 6 :Final Answer: The 90% confidence interval for the difference in proportions of employees who skip breakfast before and after the free breakfast was offered is approximately \(\boxed{(-0.0921, 0.2851)}\).