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The article "Can We Really Walk Straight?" \((\) American Journal of Physical Anthropology \([1992]: 19-\) 27) reported on an experiment in which each of 20 healthy men was asked to walk as straight as possible to a target \(60 \mathrm{~m}\) away at normal speed. Consider the following data on cadence (number of strides per second): \(\begin{array}{llllllll}0.95 & 0.85 & 0.92 & 0.95 & 0.93 & 0.86 & 1.00 & 0.92 \\\ 0.85 & 0.81 & 0.78 & 0.93 & 0.93 & 1.05 & 0.93 & 1.06 \\ 1.06 & 0.96 & 0.81 & 0.96 & & & & \end{array}\) Use the methods developed in this chapter to summarize the data; include an interpretation or discussion wherever appropriate. (Note: The author of the paper used a rather sophisticated statistical analysis to conclude that people cannot walk in a straight line and suggested several explanations for this.)

Short Answer

Expert verified
The solution to this exercise requires calculation and interpretation of several statistical measures, including central tendency (mean, median, mode), dispersion (range, variance, standard deviation), and shape of the distribution (symmetric, skewness, kurtosis). The detailed output and interpretation will depend on the outcomes of these calculations.

Step by step solution

01

Compute the Measures of Central Tendency

Calculate the mean, median, and mode for the data set. This will provide the center point of the data. To calculate the mean, add up all the data values and divide by the number of values. The median is the middle number and to find it, sort the numbers in ascending order. The mode is the value that appears the most in a data set, a data set may have one mode, more than one mode, or no mode at all.
02

Compute the Measures of Dispersion

Calculate the range, variance, and standard deviation for the data set. This will provide the spread of the data. The range can be calculated by subtracting the smallest number from the largest number. The variance is the average of the squared differences from the mean, and the standard deviation is the square root of the variance.
03

Analyze the Shape of the Distribution

Determine whether the distribution tends is symmetrical, tall or flat (kurtosis), and whether it leans to the left or right (skewness). You may want to use a histogram or box plot to visually analyze the distribution.
04

Interpret the Results

Use the statistics calculated in the previous steps to make interpretations about the data. This might involve concluding what a 'typical' stride rate per second might be, as well as the variability of stride rates. Compare your findings with the conclusions made by the initial research. Explanations and discussions should be backed up with the calculated statistics.

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Key Concepts

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

Measures of Central Tendency
In the realm of statistics, measures of central tendency are pivotal for capturing the center point of a dataset. They highlight what's typical or common in the set of numbers we're examining. Let's consider the given cadence data from the walking experiment.

To ascertain the mean cadence, we sum up all the stride rates, provided in strides per second, and then divide by the count of all provided data points. The mean offers us a single value that best represents all data points in the set. To locate the median, which is immune to extreme values, we arrange the cadence numbers in order and pick the middle value. This is particularly insightful when the data is skewed. Lastly, the mode tells us the most frequently occurring cadence rate in the list.

Understanding these measures gives us a comprehensive picture of 'average' performance within a group. However, they don't paint the entire statistical picture, as they don't take into account how much individual data points differ from the overall pattern of the dataset.
Measures of Dispersion
To fully appreciate the diversity within our dataset, we delve into measures of dispersion. These metrics illuminate how spread out our data points are around the central tendency.

The simplest measure we can calculate is the range; by subtracting the swiftest cadence from the slowest one, we obtain a rough estimate of variability. However, the range is susceptible to anomalies and doesn't tell us about the distribution between the extremes.

For a more refined approach, we compute the variance, which averages the squared deviations from the mean cadence. This gives a sense of typical variation, although it's a bit abstract since it's not in the original units. That's where the standard deviation comes to the rescue, taking the square root of the variance, bringing the dispersion measurement back into comprehensible territory—the lower the standard deviation, the tighter the data is clustered around the mean.
Shape of the Distribution
Moving beyond just the center and spread, the shape of the distribution speaks volumes about our cadence data.

By plotting the data on a histogram or a box plot, we can sketch the narrative of the distribution's symmetry or lack thereof. A perfectly symmetrical distribution means our mean and median would be identical, situated at the peak of our graph. Assessing skewness, we identify if our data tail extends more to the right (positive skew) or to the left (negative skew), which informs whether the data has a preponderance of values above or below the mean.

Furthermore, we examine kurtosis to understand how peaked or flat the distribution is. High kurtosis leads to a more distinct peak and heavier tails, indicating more outliers. Low kurtosis suggests a broader peak with less extreme outliers. Our interpretation of the shape can lead directly to assumptions about the typical stride pattern, and whether to expect consistency or a wide variety in walking cadences.
Interpretation of Statistical Results
After calculating the measures of central tendency, dispersion, and analyzing the distribution shape, we embark on the crucial final step: interpreting the statistical results from our walking experiment.

Using the mean and median, we can speculate about the 'average' cadence for individuals within the study. If the mean and median are close in value and the standard deviation is minimal, it suggests a consistent stride rate among participants. In turn, if the distribution exhibits skewness, we need to consider how it might influence the average, recognizing potential deviations in walking patterns.

Equipped with these statistics, we contrast our analysis to the original researcher’s conclusions regarding human ability to walk in a straight line. Our explanation of the data should be informed by the various statistics compiled, ranging from the typical walking cadence to the amount of variability seen. Such scrutiny demystifies complex behaviors and encapsulates the essence of statistical data analysis—bringing raw numbers to life by translating them into empirical insights.

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Most popular questions from this chapter

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