1. When the probability that your results are due to chance/sampling variation is small enough (p <.05), we reject the null, then these results are called statistically significant.
We also mentioned statistically significance during Class #14 Correlation.
2. T-test: tells us the difference between the means of two groups, and an estimate of what differences are expected from sampling variation. –> Whether the observed difference is large enough to be meaningful.
Steps of t-test:
1) The means of the two groups, take the difference
2) The pooled standard deviation, which invloves the standard deviation and sample size for both groups
[Bigger sample size gives us more power.]
3) Use information above to calculate the t score
4) Check the t Table (Morling pg 557) for the Critical Value, based on the degrees of freedom (df = n1+n2-2) and alpha level
5) The critical value is the minimum t score for us to reject the null in this case.
Set α at .05 level, if calculated t > critical t, then p < .05, the probability of getting your result given that the null is true is less than .05, reject null. Conclude that the difference is not caused by chance, but is real.
3. One-tailed t-test and two-tailed t-test: we use a one-tailed t-test when we have a directional hypothesis (X1 > X2), and a two-tailed t-test when we have a non-directional hypothesis (X1 ≠ X2).
When conducting a two-tail test, divide the alpha by 2 for the alpha on each side, then find the critical t.
PSY310 METHOD IN PSYCHOLOGICAL RESEARCH 