  First, use the Critical Significance Level (α) chosen in Step 2 and degrees of freedom (df) calculated in Step 3 (df = one less than the number of pairs) to find the Critical Value of t (tcritical) using a Critical Value Table such as the one below (e.g. if α = 0.05 and df = 15, then tcritical = 2.131).

Second, compare tcritical with the value for the t statistic calculated in Step 3.

Reject your Null Hypothesis if your calculated value is greater than or equal to the Critical value; t ≥ tcritical (significant result).

Accept your Null Hypothesis if your calculated value is less than the Critical value; t < tcritical (non-significant result).

For example, if Χ2 = 2.2 and tcritical = 2.1 then reject the Null Hypothesis.

Table of Critical Values for Critical Significance Levels (α) of 0.1, 0.05 and 0.01 for the t statistic where degrees of freedom (df) is one less than the number of pairs of data points for paired t-test.

 df α = 0.10 α = 0.05 α = 0.01 1 6.314 12.706 63.656 2 2.920 4.303 9.925 3 2.353 3.182 5.841 4 2.132 2.776 4.604 5 2.015 2.571 4.032 6 1.943 2.447 3.707 7 1.895 2.365 3.499 8 1.860 2.306 3.355 9 1.833 2.262 3.250 10 1.812 2.228 3.169 11 1.796 2.201 3.106 12 1.782 2.179 3.055 13 1.771 2.160 3.012 14 1.761 2.145 2.977 15 1.753 2.131 2.947 16 1.746 2.120 2.921 17 1.740 2.110 2.898 18 1.734 2.101 2.878 19 1.729 2.093 2.861 20 1.725 2.086 2.845 21 1.721 2.080 2.831 22 1.717 2.074 2.819 23 1.714 2.069 2.807 24 1.711 2.064 2.797 25 1.708 2.060 2.787 26 1.706 2.056 2.779 27 1.703 2.052 2.771 28 1.701 2.048 2.763 29 1.699 2.045 2.756 30 1.697 2.042 2.750 31 1.696 2.040 2.744 32 1.694 2.037 2.738 33 1.692 2.035 2.733 34 1.691 2.032 2.728 35 1.690 2.030 2.724 36 1.688 2.028 2.719 37 1.687 2.026 2.715 38 1.686 2.024 2.712 39 1.685 2.023 2.708 40 1.684 2.021 2.704

Critical values of the two-tailed t distribution generated using the TINV() function in Microsoft Excel, which returns the inverse of the Student's t-distribution. Table generated by Toby Carter.