# Assignment Worksheet 2 Solved

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## Description

Answer directly on the worksheet using the Confidence Interval Explanation file.

This assignment uses a scoring guide. Review the scoring guide on the last tab of the spreadsheet prior to beginning the assignment to become familiar with the expectations for successful completion.

Part 1 – Budget Projection:
Your friends have decided to delay your dream vacation from Worksheet 1 for five years, and you need to estimate what the cost of your trip will be by then.
Step 1: Go to the Bureau of Labor Statistics website at https://data.bls.gov/cgi-bin/surveymost?cu.
Step 2: Check U.S. All items, 1982-84=100
Step 3: Click “Retrieve Data”
Use the most recent CPI value and the CPI for the same month but five years earlier to estimate the price of your trip in five years and the five year inflation rate.

Part 2 – Data Analysis:

Enter your name in cell F1 to generate data.

You have just completed a mission to Sierra Leone. The goal of the mission was to improve the quality of water in 100 wells in a certain region. You collected data on the E. coli count from each well before and after your mission. You need to write a report on the success of the mission and for that you need to perform some statistical analysis on the data. You will be looking at the data from different perspectives to determine if the water quality has improve.

1. Calculate descriptive statistics for your data in the table provided in the Excel spreadsheet. Use the means and standard deviations of the data to decide if it appears that there has been improvement in water quality? (Fill in the before (F3:F8) and after (H3:H8) tables to the left for the descriptive statistics. The data has been named before and after for your convenience in creating formulas.)
2. The water quality is “good” if the count of E coli is 0; otherwise, the water quality is still bad. Calculate the proportion of wells with “good” water to wells whose water is not good. From this measure does it appear that the quality of water improved? Explain and use the proportions that you calculated. (In G11 and H11 calculate the percent Clean for before and after.)
3. . Look at well #1 (B2 and C2) in your data. If you drank 24oz of water how many E.coli would you ingest if you drank from the well before the mission? After the mission? (In E19 and G19 calculate how many E.coli would you ingest if you drank  24 oz. of water from Well 1 before the mission and  after the mission.)

Part 2 – Data Analysis:

You have just completed a mission to Sierra Leone. The goal of the mission was to improve the quality of water in 100 wells in a certain region. You collected data on the E. coli count from each well before (Q1) after your mission (Q2). You need to write a report on the success of the mission and for that you need to perform some statistical analysis on the data. You will be looking at the data from different perspectives to determine if the water quality has improved.

1. Since you collected water from the same source twice it makes sense to analyze the amount by which each well’s water quality improved. Calculate a data set that would measure the improvement level of each well, and the descriptive statistics for that data set, including both the standard deviation and standard error (SE) for the data set. (see section 3.5 of the textbook). Make a frequency distribution and histogram for your data. (Calculate the improvement in the water quality of each well in column D. (Difference in Level of e. Coli.) Then, fill out the two tables to the left and make a histogram of the improvement levels. (NOTE: The Standard deviation of this data set is not the same as the standard error. Use the formulas from section 3.5 of the text to calculate the standard error of the means.))
2. You have calculated one sample of 100 wells and their improvement levels. If you could take all possible samples of 100 wells, the distribution of all of those sample means would be a normal distribution. (see section 3.5). Find the 95% confidence interval of that distribution, using your sample mean as the population mean and the standard error of your sample as the population standard deviation. (Calculate the 95% confidence interval of the sampling distribution in cells F24 and  H24.)
3. Suppose that 0 was inside of the 95% confidence interval. From that measure, could you conclude that the water became cleaner? Why or why not? Suppose that 0 was outside the 95% confidence interval. From that measure, could you conclude that the water became cleaner? Why or why not?