Calculating the Mean
Average Rubythroat First Arrival Dates

Step 1) Organize the data
List the dates of first sightings. In the "order" column, list in which years hummers were seen first, second, and so on. If hummers were seen on the same date in two different years, give them the same order number.

 First Spring Hummers in _____________________ Date of 1st Sighting (by year) Order (1st, 2nd, etc) f f f f f f f f f f f f f f f f f f f f

Step 2) Determine the range (the difference between the earliest and latest dates in a set of data).

• The earliest date is _____.
• The latest date is _____.
• The range is ____ days. (Number of days from 1st to last sighting.)

Step 3) Enter data on this second chart

• Write in calendar dates, beginning with the earliest sighting (on line 1) and ending with the latest one.
• Enter all first sighting dates in the next column. When you have more than one date that's the same, it goes on the same line.
• In the last column, write in the values for each date entered. (If you have 2 dates on that line, enter the value twice, and so on.)
• Add the values for all the dates on your chart to get the total.

 Value Calendar Date Dates of First Sighting in state/hometown Values for each date 1 f f f 2 f f f 3 f f f 4 f f f 5 f f f 6 f f f 7 f f f 8 f f f 9 10 11 12 13 14 15 Total f

Step 4) Calculate the Mean (the average of all the values).
To determine the mean, take the sum (total) the values and divide by the number of years. The answer will give you the order number of the mean date.

(Total) _____ divided by (# years) ____ = _____

So mean arrival date = _____