Table of contents
- 1. Intro to Stats and Collecting Data55m
- 2. Describing Data with Tables and Graphs1h 55m
- 3. Describing Data Numerically1h 45m
- 4. Probability2h 16m
- 5. Binomial Distribution & Discrete Random Variables2h 33m
- 6. Normal Distribution and Continuous Random Variables1h 38m
- 7. Sampling Distributions & Confidence Intervals: Mean1h 3m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample1h 1m
- 10. Hypothesis Testing for Two Samples2h 8m
- 11. Correlation48m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
3. Describing Data Numerically
Mean
Problem 3.1.37
Textbook Question
Trimmed Mean Because the mean is very sensitive to extreme values, we say that it is not a resistant measure of center. By deleting some low values and high values, the trimmed mean is more resistant. To find the 10% trimmed mean for a data set, first arrange the data in order, then delete the bottom 10% of the values and delete the top 10% of the values, then calculate the mean of the remaining values. Use the axial loads (pounds) of aluminum cans listed below (from Data Set 41 “Aluminum Cans†in Appendix B) for cans that are 0.0111 in. thick. An axial load is the force at which the top of a can collapses. Identify any outliers, then compare the median, mean, 10% trimmed mean, and 20% trimmed mean.
247 260 268 273 276 279 281 283 284 285 286 288
289 291 293 295 296 299 310 504

1
Step 1: Arrange the data in ascending order. The given data set is: 247, 260, 268, 273, 276, 279, 281, 283, 284, 285, 286, 288, 289, 291, 293, 295, 296, 299, 310, 504. Sorting it in ascending order ensures that the trimming process is accurate.
Step 2: Identify and remove outliers using a standard method such as the IQR (Interquartile Range). Calculate Q1 (first quartile) and Q3 (third quartile), then compute the IQR as IQR = Q3 - Q1. Any data point below Q1 - 1.5*IQR or above Q3 + 1.5*IQR is considered an outlier. Remove these outliers from the data set.
Step 3: Calculate the 10% trimmed mean. To do this, remove the bottom 10% and top 10% of the data points. For a data set with n values, remove the lowest ⌊0.1 * n⌋ and highest ⌊0.1 * n⌋ values. Then, compute the mean of the remaining data points.
Step 4: Calculate the 20% trimmed mean. Similarly, remove the bottom 20% and top 20% of the data points. For a data set with n values, remove the lowest ⌊0.2 * n⌋ and highest ⌊0.2 * n⌋ values. Compute the mean of the remaining data points.
Step 5: Compare the median, mean, 10% trimmed mean, and 20% trimmed mean. The median is the middle value of the sorted data set, while the mean is the average of all data points. Observe how the trimmed means differ from the mean and median, and note how trimming reduces the influence of extreme values.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Trimmed Mean
The trimmed mean is a statistical measure that reduces the influence of outliers by removing a specified percentage of the lowest and highest values from a data set before calculating the mean. For example, a 10% trimmed mean involves discarding the lowest 10% and highest 10% of data points, which results in a more robust average that better represents the central tendency of the remaining values.
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Outliers
Outliers are data points that significantly differ from the other observations in a dataset. They can skew the results of statistical analyses, particularly measures like the mean. Identifying outliers is crucial as they can indicate variability in measurement, experimental errors, or novel phenomena that warrant further investigation.
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Measures of Central Tendency
Measures of central tendency, including the mean, median, and mode, summarize a set of data by identifying the center point or typical value. The mean is the arithmetic average, the median is the middle value when data is ordered, and the mode is the most frequently occurring value. Each measure provides different insights, especially in the presence of outliers, making it important to compare them for a comprehensive understanding of the data.
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