Casio 300 PLUS User Guide

20050501

7-10-1

Confidence Intervals

A confidence interval is a range of values that has a specified probability of containing the
parameter being estimated.

A confidence interval that is too broad makes it difficult to get an idea of where the parameter
(actual value) is located. A narrow confidence interval, on the other hand, limits the
parameter range and makes it possible to obtain highly accurate results.

The commonly used confidence levels are 68%, 95% and 99%. Raising the confidence level
broadens the confidence interval. Conversely, lowering the confidence level narrows the
confidence interval, but it also creates the risk that parameters will be missed. With a
confidence interval of 95%, for example, there is a 5% probability that a parameter will not be
within the interval.

The following is a list of confidence intervals and a description of what each obtains.

1-Sample 

 Interval

Obtains the confidence interval for the population mean when the 
population standard deviation is known. 

2-Sample 

 Interval

Obtains the confidence interval for the difference between population 
means when the population standard deviations of two populations are 
known. 

1-Prop 

 Interval 

Obtains the confidence interval of the proportion of successes in a 
population.

2-Prop 

 Interval 

Obtains the confidence interval of the difference between the 
proportions of successes of two populations. 

1-Sample 

 Interval

Obtains the confidence interval for the population mean when the 
population standard deviation is unknown. 

2-Sample 

 Interval 

Obtains the confidence interval for the difference between two 
population means when the population standard deviations are
unknown. 

k General Confidence Interval Precautions

If you input a C-Level (confidence level) value in the range of 0 < C-Level < 1, the value you
input is used.  To specify a C-Level of 95%, for example, input “0.95”.