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95% CIs for Mean Calculation in the Explore function in Analyze, Descriptive Statistics

  • 1.  95% CIs for Mean Calculation in the Explore function in Analyze, Descriptive Statistics

    Posted Thu October 03, 2024 09:04 AM

    I was trying to calculate the 95% confidence interval for the mean for a set of 40 numbers 

    11

    23

    25

    27

    21

    23

    26

    18

    17

    16

    23

    26

    26

    23

    16

    20

    24

    17

    27

    17

    16

    25

    19

    24

    20

    17

    24

    19

    26

    22

    15

    24

    21

    22

    21

    18

    22

    24

    16

    18

    In the SPSS Statistics Analyze --> Descriptive Statistics --> Explore function, the 95% CI calculated was [19.7154, 22.2346]. But using the 95% CI formula, which is the mean + 1.960*(SE), I calculated [19.75445, 22.19555]. There were some discrepancies between the two calculations.

    I tried again with 40 other numbers:

    51

    35

    32

    33

    38

    32

    27

    33

    32

    25

    39

    23

    23

    36

    30

    34

    38

    39

    18

    34

    37

    28

    38

    29

    34

    33

    37

    24

    19

    35

    27

    27

    20

    24

    33

    27

    38

    20

    29

    35

    SPSS calculated the 95% CI as [28.97, 33.33] but the correct 95% CI is [29.03701, 33.26299]. SPSS seemed to systematically extend the 95% CI for some reason. 

    Can anyone explain what formula did SPSS use for the 95% CI for the mean? I'm a bit confused.



    ------------------------------
    Shun Hei Caleb Lin
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  • 2.  RE: 95% CIs for Mean Calculation in the Explore function in Analyze, Descriptive Statistics
    Best Answer

    Posted Thu October 03, 2024 11:50 AM
    The Explore (EXAMINE) procedure correctly uses the t distribution, which has a slightly larger CI to account for the standard deviation being estimated. You used the normal distribution.

    You can find the formulas for all the SPSSD statistics in the Algorithms manual, which you can find via Help > Doc in pdf format.

    --



    Original Message


  • 3.  RE: 95% CIs for Mean Calculation in the Explore function in Analyze, Descriptive Statistics

    Posted Thu October 03, 2024 09:41 PM

    Ahh, gotcha. That's really helpful. Thanks! 



    ------------------------------
    Shun Hei Caleb Lin
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    Original Message


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