Due date Statistics 2 – Activity 2

Due date? For pregnant women, the due date is the finishing line for what seems a long nine months. The ‘due date’ increasingly becomes the focus of their lives. But how accurate is the ‘due date’?

Read the report before continuing Due date – why bother if it is highly unlikely that the baby will arrive on that day? A recent report suggests that only 5% of babies are actually born on their due date – and that the length of pregnancy varies by around five weeks.

The data Distribution of the length of ovulation-based gestation (Early pregnancy study) This data is available on the spreadsheet data_gestation.xlsx

By drawing a cumulative frequency graph, find the five key measures for this data. Draw a box plot of your results and comment on your findings. What difference does it make if we ignore the six premature babies? Minimum (Q 0 ) Lower quartile (Q 1 ) Median (Q 2 ) Upper quartile (Q 3 ) Maximum (Q 4 )

Further thoughts… From your cumulative frequency graph, estimate the percentage of babies born: a) within 5 days of the median value b) within 10 days of the median value c) within 18 days of the median value What difference does it make if we ignore the six premature babies?

An alternative approach Using all of the data, calculate both the mean length and standard deviation of ovulation – conception. It is much easier if you use the spreadsheet. Mean x or μ = Standard deviation σ = Now find the percentage of results a) within 1 standard deviation of the mean b) within 2 standard deviations of the mean c) within 3 standard deviations of the mean What difference does it make if we ignore the six premature babies? Do your findings support the claims made in the article?

A natural phenomenon There are many cases where the data tends to be around a central value with no bias left or right, and it gets close to a ‘Normal Distribution’ like this: Interestingly, ‘normally distributed’ data has some interesting characteristics: The curve is often described as bell-shaped mean = median = mode It is symmetrical about the mean 50% of the data is below the mean and 50% of the data is above the mean.

A natural phenomenon About 68% of values drawn from a normal distribution are within one standard deviation σ away from the mean; about 95% of the values lie within two standard deviations; and about 99.7% are within three standard deviations. This fact is known as the (empirical) rule, or the 3-sigma rule. Normal distribution – Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Normal_distribution

Suggestion Follow this activity with ‘Baby boom’

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