## ← Independent Samples - Intro to Inferential Statistics

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Showing Revision 5 created 05/25/2016 by Udacity Robot.

1. Welcome to Lesson 11. In Lesson 10, you learned about dependent samples or
2. repeated measures. Just to refresh your memory, that could be where we give the
3. same person two different conditions to see how they react to each one. Maybe a
4. control and then a treatment, or maybe two types of treatments. Or, this could
5. be longitudinal, where we measure some variable at some point in time, and then
6. again at another and see if the variable changes. Or this could be a pre-test
7. and post-test. What was the measurement of a variable before and after a
8. treatment? These are just a few situations in which we would use dependent
9. samples. This type of research design is really useful because it controls for
10. indivdual differences. In other words, if we gave someone some kind of
11. treatment, then those same individual differences will be present the next time
12. we give that same treatment. That way we can see how two different treatments
13. play out under the same conditions. Because there's controls for individual
14. differeneces, we could then use fewer subjects. And this is more cost
15. effective, less time consuming, and generally less expensive. However, there
16. are also a few disadvantages. One of which, is carry-over effects. For example,
17. let's say we have this new method of teaching math. You want to know if it's
18. going to be effective. If you use the same group of students to test this new
19. teaching method, inevitably, they're going to be better at math the second time
20. around. So, if the first time we teach them one way, and then the second lesson
21. we teach them a different way, they'll already be better at math from learning
22. it the first time. Then we don't know if the results after the second treatment
23. are due to the fact that it was effective or due to the fact that they've
24. learned math before. That's just one example. The second measurement can be
25. affected by the first treatment. And the order in which we give the treatment
26. might influence the results. For example, say we want to test two types of
27. pills. What if the first pill has some kind of interaction with the second
28. pill? And so, by taking it in that order they affect the results. Therefore, in
29. this lesson, you're going to learn about independent samples. Whereas,
30. dependent samples deals with within subject designs, independent samples deals
31. with between subject designs. In this case, the advantages of dependent samples