Week 3- T tests Flashcards
What are some of the assumptions that need to be met in order for independent samples t-tests to work properly?
1- The IV is a factor with two levels (e.g., male vs female, associate prof vs prof, default vs no default, etc.)
2- The DV is a numerical variable (not ordinal)
3- The DV is fairly normal (parametric assumption #1)
What is the difference between a one-tailed and a two-tailed test?
One tailed is directional (i.e., you expect that one measurement is greater or lesser than the other). Two tailed is non-directional
Is a one-tailed test more, or less conservative than a two-tailed test? Why is that?
Less conservative. The t critical threshold to cross the boundary of significance is smaller.
Maria wants to examine whether employee satisfaction with the legacy payroll system is less than with the new and shiny online web-based system.
Maria wants to increase the statistical power of her test, as well as reduce the amount of participants she will need. Should she use two sample or paired sample design?
Paired sample is more statistically powerful and requires less participants.
Maria ends up using a two sample (independent samples) design. She chooses to use a t-test. Assuming the usual 5% significance threshold, she reports that t(258) = 2.59, p < 0.05. Did Maria find enough evidence to support her hypothesis? Why?
Yes, the p-value is less than 5% (p < 0.05). Therefore, she can reject the null hypothesis and say that employees are more satisfied with the new payroll system than the legacy system.
Maria wants to make her test more conservative and changes the significance threshold from 0.05 to 0.01. Her p-value was actually 0.02. Did she still find evidence to support her hypothesis given her new significance threshold?
No. Now that she made her test more conservative, she can no longer reject the null, since the p-value is 0.02
Maria used Cohen’s d and found d = 0.3. How large is the effect of the IV on the DV?
Small effect (up to 0.5). If Maria uses a threshold of 0.05, then she found a small but significant effect of the system on satisfaction (satisfaction ~ system)
