Trend-Line Analysis

In a trend-line analysis, you are performing a linear regression calculation on data that is collected at regular, sequential intervals. Each new x value is one greater than the previous x value. The calculator automatically increments the initial value of x so that you do not have to enter subsequent x values.

Entering the Data

To enter data for a trend-line analysis:

Enter the first data values as described in "Entering and Removing 2-Variable Data"; enter x and press [ x~t ], then enter y and press [ ∑+ ].
Enter only the y value for the remaining data values. The calculator automatically enters the corresponding x value.

Note:

If any of the remaining data values are not sequential, be sure to reenter the new x value.

A trend line applies only to single occurrence data, so the { FRQ } key is not part of trend line data entry.

Removing Data

To remove a data pair just after it is entered, press [ INV ][ ∑+ ]. The calculator removes the last x and y values and automatically decrements the contents of the t-register in preparation for the next entry.

To remove an entry at a later time, use the procedure described in "Entering and Removing 2-Variable Data".

Example

A company has the following annual profits:

Year(x)	Profit in Millions(y)
1971	-2.1
1972	-0.3
1973	0.8
1974-1980	inactive
1981	2.9
1982	2.8
1983	3.6
1984	4.0
1985	4.7

Use the data from the above table to perform a trend-line analysis. How much profit can the company expect to make in 1986, and when will it break the $6 million mark?

Procedure	Press	Display
Clear display	[ CLEAR ]
Clear registers and select 2-variable	[ STAT ] { CLR } { CS2 }
Initial value of x (1971)	1971 [ x~t ] 2.1 [ +/- ] [ ∑+ ]
1972 profit	.3 [ +/- ] [ ∑+ ]
1973 profit	.8 [ ∑+ ]
Skip to 1981	1981 [ x~t ] 2.9 [ ∑+ ]
1982 profit	2.8 [ ∑+ ]
Incorrect 1983 profit	3.4 [ ∑+ ]
Remove last entry	[ INV ] [ ∑+ ]
1983 profit	3.6 [ ∑+ ]
1984 profit	4 [ ∑+ ]
1985 profit	4.7 [ ∑+ ]
Correlation	{ --> } { r }
1986 predication	1986 { y' }
Year of $6 million profit	6 [ INV ] { y' }