Emergence
Early or Late? What's the Range, Median and Mean?
Are tulip
gardens emerging and blooming early or late this year? Let's take a look
at gardens in one of our coldest regions: Anchorage, AK. Data from several
years may give us new insights for making accurate predictions.
 Range:
The difference between the earliest and latest dates in a set of data.
 Median:
The median is the 50th percentile. The date in an ordered set of data
such that half of the dates are earlier and half of the dates are later.
Half the values are larger than the median, and half are lower. If there
are an even number of values, the median is defined as the average of
the two middle values.
 Mean:
The mean is the average of all the values. It's the most common measure
of center. To determine the mean, find the sum of the values in the
set, then divide by the number of values.
Try
This!
Here are emerging dates for tulips in Anchorage: 3/20/00, 5/07/99, 4/13/98,
and 5/05/97. Take a close look at the data:
 Arrange
the data in order from earliest to latest date of sighting.
 Count
the number of days between the earliest and latest arrival dates. This
difference is the range of emerging dates for Anchorage.
 Next figure
the median emerging date. Your data are already in order, so you can
see on which date half of the records are earlier and half of the records
are later. (Because there is an even number of records, you'll need
to find the average of the two middle values.)
 Finally,
calculate the mean emerging date. (The mean is the concept most people
think of as the "average.") When using calendar dates, this
can be tricky. Before reading the example on the worksheet, challenge
yourself to think this through!
Now, based
on what you know to be the mean date of emergence, what do you think will
happen in 2001?
Journaling Questions
 After
calculating the mean, or average date of tulip emergence in Anchorage,
what do you predict this year's emergence date will be?
 If you
think it will be different than the mean, what factors this year might
lead you to your prediction?"
National
Science Education Standards
Science
as Inquiry
Develop descriptions, explanations, predictions, and models using evidence.
(58)
Use math
in all aspects of scientific inquiry. (58)
National
Math Standards
Data Analysis
and Probability
Select and use appropriate statistical methods to analyze data.
Develop and
evaluate inferences and predictions that are based on data.
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