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Ch. 2 - Descriptive Statistics
Larson - Elementary Statistics: Picturing the World 8th Edition
Larson8th EditionElementary Statistics: Picturing the WorldISBN: 9780137493470Non è quello che usi tu?Cambia libro di testo
Capitolo 2, Problema 2.5.41

Graphical Analysis In Exercises 41 and 42, the midpoints A, B, and C are marked on the histograms at the left. Match them with the indicated z-scores. Which z-scores, if any, would be considered unusual?


z = 0, z = 2.14, z = −1.43


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Step 1: Understand the problem. The histogram represents test scores, and the midpoints A, B, and C are marked. We need to match these midpoints with the given z-scores (z = 0, z = 2.14, z = −1.43) and determine which z-scores are unusual. Recall that z-scores measure how many standard deviations a data point is from the mean.
Step 2: Identify the mean and standard deviation. The histogram shows a distribution of scores. The mean is likely near the center of the distribution, which corresponds to the midpoint B (score = 63). The standard deviation can be estimated based on the spread of the data.
Step 3: Match z-scores to midpoints. A z-score of 0 corresponds to the mean, so midpoint B (score = 63) matches z = 0. A z-score of −1.43 indicates a value below the mean, so midpoint A (score = 53) matches z = −1.43. A z-score of 2.14 indicates a value above the mean, so midpoint C (score = 78) matches z = 2.14.
Step 4: Determine unusual z-scores. A z-score is considered unusual if it is less than −2 or greater than 2. In this case, z = 2.14 is greater than 2, so it is considered unusual. The other z-scores (z = 0 and z = −1.43) are not unusual.
Step 5: Summarize the findings. Midpoint B corresponds to z = 0, midpoint A corresponds to z = −1.43, and midpoint C corresponds to z = 2.14. The z-score of 2.14 is considered unusual because it is greater than 2.

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Z-scores

A z-score indicates how many standard deviations an element is from the mean of a dataset. It is calculated by subtracting the mean from the value and then dividing by the standard deviation. Z-scores help in understanding the relative position of a score within a distribution, allowing for comparisons across different datasets.
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Z-Scores From Given Probability - TI-84 (CE) Calculator

Unusual z-scores

In statistics, z-scores that are greater than 2 or less than -2 are often considered unusual, as they lie outside the typical range of values in a normal distribution. This threshold indicates that the score is significantly different from the mean, suggesting it may represent an outlier or an exceptional case within the data.
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Histograms

A histogram is a graphical representation of the distribution of numerical data, where the data is divided into bins or intervals. The height of each bar represents the frequency of data points within that interval. Histograms provide a visual summary of the data's distribution, helping to identify patterns, trends, and potential outliers.
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Intro to Histograms
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