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One Tailed T Test SPSS

  • 1.  One Tailed T Test SPSS

    Posted Fri September 18, 2020 12:34 PM
    It is my understanding that I cannot run a one-tailed T Test in SPSS. My best option is two run a two tailed T test, and divide the p.value by two? Additionally, the sign (-, +) in front of the T value will give me insight into the direction of my results. 

    Please advise if this is correct. 

    Given this, can I assume all output for a two tailed t test will be the same for a one tailed? T statistic, the cohen's d, confidence intervals, and group means? 


    Additionally, with cohen's d - is the manual calculation the same? 

    Thanks! 



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    ss814
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  • 2.  RE: One Tailed T Test SPSS

    Posted Fri September 18, 2020 12:51 PM
    A one-tailed t test is exactly the same as a two-tailed test except that the critical region is only  on one side.  Similarly, the CI would be one sided.

    In Statistics V27, the effect size according to several different statistics is provided by the t test procedure.  In older versions, you would need to  calculate this by hand or see C18 in SPSS Statistics for Data Analysis and Visualization by McCormick, Salcedo et al.

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    Jon Peck
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