2. Describing Data with Tables and Graphs
Frequency Distributions
2:37 minutesProblem 2.1.12
Textbook Question
In Exercises 9–12, using a loose interpretation of the criteria for determining whether a frequency distribution is approximately a normal distribution, determine whether the given frequency distribution is approximately a normal distribution. Give a brief explanation.
Blood Platelet Counts of Females Refer to the frequency distribution from Exercise 8
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Step 1: Review the frequency distribution table provided. The table lists blood platelet counts of females in intervals (100–199, 200–299, etc.) along with their corresponding frequencies.
Step 2: Check for symmetry in the distribution. A normal distribution typically has frequencies that increase to a peak and then decrease symmetrically. Observe whether the frequencies rise to a peak and then fall off in a balanced manner.
Step 3: Identify the peak frequency. In this case, the interval 200–299 has the highest frequency (92). Compare the frequencies of intervals on either side of the peak to see if they decrease symmetrically.
Step 4: Look for gaps or irregularities. Note that the interval 400–499 has a frequency of 0, which disrupts the smooth decline expected in a normal distribution. This gap suggests the distribution may not be normal.
Step 5: Consider the shape of the distribution. Based on the frequencies, the distribution appears skewed rather than bell-shaped, as the frequencies do not decrease symmetrically around the peak. Provide an explanation that the distribution is not approximately normal due to the lack of symmetry and the presence of gaps.
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