1 / 29

Lab IV: Outline, Part 1

Lab IV: Outline, Part 1. Use of correlated versus independent t -tests – Sample Experiment Introduction to a web-based stats program: Vassarstats How to graph Ms and SDs, an example. The Terrible t ’s. Independent and Correlated (Paired) t -tests.

bern
Download Presentation

Lab IV: Outline, Part 1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lab IV: Outline, Part 1 • Use of correlated versus independent t-tests – Sample Experiment • Introduction to a web-based stats program: Vassarstats • How to graph Ms and SDs, an example

  2. The Terrible t’s Independent and Correlated (Paired) t-tests

  3. I pity the fool who doesn’t know when to use correlated vs. independent t-tests!

  4. Sample Experiment: t-test Examples • Hypothesis 1: Exposure to bright light will increase gill flare in male Betta splendens. • Hypothesis 2: Male Betta splendens exposed to bright light will have longer gill flare durations than those not exposed to bright light.

  5. Sample Experiment: t-test Examples • Subjects: 4 adult male Betta splendens (A, B, C, D) A

  6. B D A C Exposed fish to each other for 10 min, recorded gill flare Trial 1

  7. Trial 1 Gill Flare (/10 min.) = baseline duration of gill flare

  8. Exposed Fish A & Fish C to bright light for 5 min. (no light) (no light) B D C A

  9. B D A C Exposed fish to each other for 10 min, recorded gill flare Trial 2

  10. Trial 2 Gill Flare (/10 min.) = duration of gill flare after light/no light

  11. Fish No Light (Before) Light (After) A 100 s 200 s C 90 s 185 s Hypothesis 1: Exposure to bright light will increase gill flare in male Betta splendens. *We want to compare each fish’s score on one condition (“before exposure”) to its score on another condition (“after exposure”)

  12. Fish No Light (Before) Light (After) A 100 s 200 s C 90 s 185 s Correlated (or Paired) t-test • Scores between conditions are for same subject • i.e., Fish A has a score for both “light” and “no light”, and Fish B has a score for both conditions • Hence, scores are said to be “paired” or “correlated”)

  13. t-tests and procedures How to use Vassarstats for t-tests • http://faculty.vassar.edu/lowry/VassarStats.html

  14. = Number of rows 2

  15. Row 1 = Fish A’s scores Row 2 = Fish C’s scores Xa = before light exposure Xb = after light exposure

  16. Because our hypothesis was unidirectional (meaning we predicted change in a single, specific direction), we can use the one-tailed value.

  17. Now just copy and paste

  18. How to Report Results: Examples • “Exposure to bright light significantly increases gill flare duration in male Betta splendens(t = -39, df = 1, p < .05) .” Must also include Ms and SDs in a table or graph. • “Gill flare duration after light exposure (M = 192.5, SD = 10.61) was significantly greater than before light exposure (M = 92.5, SD = 7.07); t(1) = -39, p < .05.”

  19. Subject Light Subject No Light A 200 s B 130 s C 185 s D 125 s Hypothesis 2: Male Betta splendens exposed to bright light will have longer gill flare durations than those not exposed to bright light. *Across conditions, we are comparing the scores of two different fish; hence, the scores are independent of each other

  20. Subject Light Subject No Light A 200 s B 130 s C 185 s D 125 s Independent t-test • The scores between the two conditions are from different subjects, which makes them independent • The scores in the “Light” condition are not correlated with scores in the “no light” condition

  21. How many scores are in each column? (If unequal, pick larger.) 2

  22. Xa = Light Xb = No Light

  23. How to Report Results: Examples • “Male Betta splendens that were exposed to bright light (M = 192.5, SD = 10.61) flared their gills for longer durations than those not exposed to bright light (M = 127.5, SD = 3.54);t(2) = 8.22, p < .05.” • Or, can give Ms and SDs in a table or graph.

  24. How to graph Ms and SDs for Duck Lab

  25. HINT: The columns correspond to those used for your t-test… SD for C2 SD for C1 Mean for C2 Mean for C1

More Related