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2 Proportion Z Interval Calculator

Confidence interval for the difference of 2 proportions.

screenshot

 

Example

Find the 0.95 confidence interval for two proportions, 49 successes in 61 trials and 38 successes in 62 trials

Value Keystroke Display Description
.95 C Level 0.95 Stores the C Level value.
61 n1 61.00 Stores the n1 value.
49 ÷ ROLL p̂1 0.8033 Stores the  p̂1 value.
62 n2 62.00 Stores the n2 value.
38 ÷ ROLL p̂2 0.6129 Stores the  p̂2 value.
  Z Int 0..3140 Calculates the Z Interval

The keystrokes '÷ ROLL p̂1' are in CHN calculation mode. Since the 'n' value was just entered, tapping 'ROLL' saves you from having to re-enter the n value.
In ALG calculation mode, the keystrokes would be '÷ rgx p̂1'.
In RPN calculation mode, the keystrokes would be 'SWAP ÷ STO p̂1'.

This calculator also calculates the upper and lower limits and enters them in the stack.
By returning these values to the stack you can use them for other calculations without having to write them down and re-enter them.

Value Keystroke Display Description

ROLL 0.03337 The lower limit

ROLL 0.3474 The upper limit

The History Detail

2 Proportion Z Interval
         0.1904 : The difference in p estimates.
         0.3474 : The upper limit.
        0.03337 : The lower limit.
         0.9500 : The confidence level.
          61.00 : The number of trials 1 , n1.
         0.8033 : The proportion estimate 1, p̂1.
          62.00 : The number of trials 2, n2.
         0.6129 : The proportion estimate 2, p̂2.
         0.3140 : The Confidence Interval on the Difference in Population Proportion.

Note that you can enter a "Z Int" value and solve for the C Level.

Reference:

Confidence Interval - Wikipedia