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A survey conducted in May 2010 asked 1917 cell phone users to estimate, on average, the number of text messages sent and received per day. (a) Do you expect the distribution of number of text messages per day to be symmetric, skewed to the right, or skewed to the left? (b) Two measures of center for this distribution are 10 messages and 39.1 messages. \({ }^{32}\) Which is most likely to be the mean and which is most likely to be the median? Explain your reasoning.

Short Answer

Expert verified
a) The distribution of number of text messages per day is expected to be skewed to the right. b) The mean will most likely be 39.1 messages and the median will be 10 messages.

Step by step solution

01

Understanding data distribution

Symmetry in data distribution means that the values are evenly distributed on both sides of the average. A skew to the right (positive skew) indicates that there are a number of outlying high values. A skew to the left (negative skew) means that there are a number of outlying low values.
02

Predicting text message distribution

Considering the variable which is the number of text messages sent and received per day, it's reasonable to assume that the distribution of this variable would be skewed to the right. This is because while most people might send/receive a moderate number of texts, there will be some who send/receive a large number of texts, creating the skewness.
03

Understanding mean and median

The mean is often susceptible to being affected by extreme values (outliers), hence in a right-skewed distribution it will likely be greater than the median. On the other hand, the median, being the middle number in a sorted list of data, will be less affected by extreme values, hence will be smaller in a right skewed distribution.
04

Analyzing the given measures of center

In this case, given the two measures of center, 10 and 39.1, the indicator that most likely represents the mean would be 39.1 (the higher value) and the median would be 10 (the lower value). This is because of the presumption of a right-skewed distribution based on the nature of the data.

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Key Concepts

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

Understanding Skewed Distributions
Data distributions can come in various shapes, one of which is skewness. Skewed distributions do not symmetrically center around their average. Instead, they have tails that either lean towards higher or lower values. A **right-skewed** distribution has a long tail extending towards the right. This occurs when there are few unusually high values in the data set. For example, if a small number of people send hundreds of messages each day, compared to the majority who send far fewer, the distribution of text messages will appear right-skewed. Such outliers can significantly affect data interpretation and analysis. On the contrary, a **left-skewed** distribution has a long tail extending towards the left, indicating a few extremely low values pushing the majority of the data points centrally or to the right. Recognizing the direction of skewness is critical for data analysis, allowing for more accurate data interpretation.
Mean and Median Comparison
When analyzing skewed data distributions, it's important to compare the mean and the median. Both are measures of central tendency, but they behave differently in skewed environments. The **mean** is the average of all data points and is sensitive to outliers. In a right-skewed distribution, it's typically higher than the median because the outliers raise the average. The **median**, however, is the middle value in an ordered dataset. It is more robust against outliers, maintaining stability even when extreme values exist. Therefore, in a right-skewed distribution, the mean will usually be greater than the median. For the exercise, given the measured values of 10 and 39.1, it's reasonable to assume that 39.1 is the mean, inflated by higher text extremes, while 10 represents the median.
Role of Statistical Reasoning
Statistical reasoning provides the tools needed to analyze, interpret, and make predictions based on data. It allows us to make sense of distributions, whether symmetric or skewed, and to choose appropriate measures of center based on the data's nature. This involves logical deductions and careful analysis to understand what the data is signaling about the population or process being studied. The key goal is to draw valid conclusions. For instance, in the text message scenario, identifying the skewness helps in determining the most likely measures of central tendency. Such reasoning builds on a solid understanding of statistical concepts like outliers, variability, and central tendency. It involves questioning assumptions and sometimes reevaluating them based on new evidence or broader data contexts. In doing so, it ensures a deeper understanding of data patterns and underlying trends.

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