USING THE CASIO FX-115 FOR BASIC STATISTICS

Starting in 1998, Newcastle University Examinations Regulations will permit the use of only two approved hand calculators in exams - the Casio FX-82 and the Casio FX-115. In MSCM we recommend the FX-115 which offers linear regression functions as well as standard deviation functions which are also available on the FX-82. Note that linear regression calculations are employed in a number of compulsory undergraduate modules within the Department which have a formal examination, including Numerical Methods (MSM231) and Fisheries Biology and Aquaculture (MSM222), and are also likely to be needed on several others.

The FX-115Ws, a solar powered version, is normally available for sale in the Department for £13 (see Dr Bythell, R360 Ridley Building, email j.c.bythell@ncl.ac.uk).

STANDARD DEVIATION

To calculate the standard deviation of a sample:

1. Enter standard deviation mode by pressing [MODE][2]
2. Make sure to clear the memory register by pressing [SHIFT][AC]
Enter the value of each data point followed by [M+] (marked 'DATA' in blue). Repeat for all values in the sample.

The data are now stored and will be held until you clear or overwrite the memory registers. Various sample statistics can be called up, but first check the sample size (n) to make sure that you have entered the correct number of data points:

To find sample size (n): press [RCL][3]


To find the sample mean : press [SHIFT][1]
To find the sample standard deviation: press [SHIFT][3]

You can find the standard error by dividing the standard deviation by the square root of n


Multiply the standard error by t (from tables, for n - 1 degrees of freedom and p = 0.05) to find the 95% confidence interval.

LINEAR REGRESSION

To carry out least-squares linear regression (type 1):

Enter LR (linear regression) mode by pressing [MODE][3]


Make sure to clear the memory register by pressing [SHIFT][AC]
Enter the value of the first independent (x) data point followed by [{(- -] (marked 'xD,yD' in blue), then enter the corresponding dependent (y) data point followed by [M+] (marked 'DATA' in blue). Repeat the process for each x,y pair.

The data are now stored and will be held until you clear or overwrite the memory registers. Various linear regression statistics can be called up, but first check the sample size (n) to make sure that you have entered the correct number of data points:

To find sample size (n): press [RCL][3](note this is number of pairs of data)


To find the intercept (a): press [SHIFT][7](marked 'A' in brown)
To find the slope (B): press [SHIFT][8](marked 'B' in brown)
To find the correlation coefficient (r): press [SHIFT][9](marked 'r' in brown)

Note that for linear regression analysis you would normally quote the regression coefficient (r2): simply square the correlation coefficient (press [SHIFT][9][X2]).