Calcluating the Mean
Tulip Emerging Dates

People always wonder, when will our tulips emerge? You can use historic event records collected in a single place to calculate the "mean" date.

The mean date is the 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.

To calculate the mean using calendar dates, it helps to rank them, or put the dates in order, and to assign each date a number. The example on the chart below uses the emerging dates for Pequot Lakes, MN. Their tulips emerged on 2/23/98, 3/24/97, 3/25/00, 4/01/99, 4/05/01, 4/18/03, and 4/22/02.

• Put the dates of emerging tulips in order by month and day. (This has been done for you.)
• Enter dates on the chart calendar. (Earliest date goes on the first line, then count down days down til you reach the next date.) Use the order number beside each date for its value.
• Add all the values for all the dates
• Then divide by the number of emerge dates. The result is the order number. Find the order number on the chart and calculate the date. This is the mean arrival date.
• The chart has space for you to calculate the mean emerging date for your home town.

 Order (value) Date of Emerging Tulips in Pequot Lakes, MN Date of Emerging Tulips in My Home Town 1 2/23/98 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 3/24/97 31 3/25/00 32 33 34 35 36 37 4/01/01 38 39 40 41 4/05/01 42 43 44 45 46 47 48 49 50 51 52 53 54 4/18/01 55 56 57 58 4/22/01