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A student asked her coworkers, parents, and friends, "How many friends do you have on Facebook?" She summarized her data and reported that the average number of Facebook friends in her sample is 170 with a standard deviation of \(90 .\) The distribution had a median of 120 and a mode of 105 . a. Based on these statistics, what would you surmise about the shape of the distribution? Why? b. Does the empirical rule apply to these data? Why or why not?

Short Answer

Expert verified
a. The distribution is right-skewed because the mean is greater than the median. b. The empirical rule does not apply, as the data is not normally distributed.

Step by step solution

01

Analyze the relationship between mean, median, and mode

To determine the shape of the distribution, compare the mean, median, and mode. A symmetrical distribution will have the mean, median, and mode roughly equal. Here, the mean is 170, the median is 120, and the mode is 105. Since the mean is significantly higher than both the median and the mode, this suggests that the distribution is right-skewed (positively skewed).
02

Define the empirical rule

The empirical rule states that for a normal distribution, approximately 68% of the data falls within 1 standard deviation from the mean, 95% within 2 standard deviations, and 99.7% within 3 standard deviations. This rule applies well to symmetric, bell-shaped distributions.
03

Evaluate the applicability of the empirical rule

Since our distribution is right-skewed, it does not have the symmetric, bell-shaped curve required by the empirical rule. Therefore, we cannot confidently apply the empirical rule to this data set, as it may lead to incorrect assumptions about the percentage of data within each range of standard deviations.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Distribution Shape
When analyzing data, understanding the distribution shape is vital as it tells us how the values in the dataset are spread. The shape helps us anticipate patterns and behaviors of the data. In this scenario, we examine the relationship between the mean, median, and mode to determine the distribution shape. The mean is calculated as 170, the median is 120, and the mode is 105. This indicates a right-skewed distribution, meaning there are more values concentrated on the lower end, with fewer but larger values stretching out to the right.
  • Mean greater than median and mode: suggests a right-skew.
  • Mean less than median and mode: suggests a left-skew.
  • Mean roughly equal to median and mode: indicates a symmetric distribution.
Understanding these concepts helps with predicting how the rest of the data might be spread, which is essential for making informed analyses and decisions.
Empirical Rule
The empirical rule, often called the '68-95-99.7 rule', is a handy guideline used to understand the distribution of data points in a normal distribution. It conveys that: - About 68% of data falls within one standard deviation () of the mean. - About 95% of data falls within two standard deviations (7) of the mean. - About 99.7% of data falls within three standard deviations (7) of the mean. This rule is applicable only when the distribution is bell-shaped and symmetric. Thus, for a skewed distribution, as seen in this example, the empirical rule does not fit well. This is due to the lack of symmetry and presence of skew, leading to potential inaccuracies in data interpretation if the rule is applied.
Standard Deviation
Standard deviation is a crucial statistic that quantifies the amount of variation in a dataset. It shows how much individual data points differ from the mean of the data. In our example, the standard deviation is 90, indicating that there is a relatively wide spread of data points around the mean of 170.
  • Low standard deviation: indicates data points are close to the mean.
  • High standard deviation: suggests data points are spread out over a wide range.
Standard deviation enables analysts to understand data variability and reliability. In skewed distributions, a high standard deviation like 90 can indicate a few extreme values which are pulling the mean away from the median and mode, further reinforcing the insights about distribution shape.
Mean, Median, Mode Analysis
The analysis of the mean, median, and mode offers critical insights into assessing the tendencies within your dataset. - **Mean**: It is the average value, providing a central value for the data set. In skewed distributions, it could be misleading as it can be heavily affected by outliers or extreme values. Here, the mean is 170. - **Median**: This is the middle point in the data, representing the value that splits the dataset in half. It is less susceptible to extreme values, offering a better sense of central tendency when a dataset is skewed. In this case, the median is 120. - **Mode**: The mode is the most frequently occurring value in the dataset. It can highlight common values within the data that may not align with the mean or median, as seen with a mode of 105. Understanding these measures collectively allows for a more comprehensive picture of the dataset's characteristics and potential distributions, aiding in accurately identifying the data's tendencies and skewness.

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