Calculations Example of Mann Whitney U Test A

Calculations Example of Mann Whitney U Test A psychology teacher wanted to compare the effectiveness of two A Level textbooks in making psychology easy and fun to study. The teacher decided to conduct research with students on the course to decide which new books to choose. On a piece of paper, students had to rate (out of 10, with 10 being “We love this textbook – BUY BUY”) the overall likelihood of choosing the student-centred psychology textbook. Out of 12 participants, 6 of the participants gave ratings for one of the textbooks (Textbook A), and the other 6 participants gave ratings for the other textbook (Textbook B).

Tied ranks Rank Textbook Rating 1. 5 A 2 3 A 3 4 A 4 5. 5 A 5 5. 5 B 5 7. 5 A 6 7. 5 B 6 9 B 7 10 B 8 11 B 9 12 B 10

Rank Textbook Rating 1. 5 A 2 3 A 3 4 A 4 5. 5 A 5 5. 5 B 5 7. 5 A 6 7. 5 B 6 9 B 7 10 B 8 11 B 9 12 B 10

Formula time R 1 = sum of ranks in condition 1 R 2 = sum of ranks in condition 1 = number of ppt in condition 1 n 2 = number of ppt in condition 2 U = observed or calculated value

Finding the critical value

Man Whitney U In order to determine whether this research is significant, the observed value has to be equal or less than the critical value Which means the p = <0. 05 Or that the probability of the results being due to chance is 5% or less. Or that the probability of the results being due to the IV is 95% or above

Mann Whitney U summary • Independent measures design Observed/ calculated value • Rank (look out for tied ranks) • Sum the ranks • Formula using the smallest rank Critical value • Look up table The observed value < critical value for p = 0. 05 or The observed value has to be equal or less than the critical value for their to be a 5% chance of less that the results are due to chance.

A researcher hypnotised that children will play with a toy for longer if they have seen a child of the same gender playing with a toy previously. He showed 6 children a video of the same gender as themselves playing with a toy and 6 children a video of a child of the other gender to themselves playing with the same toy. He then gave each child the opportunity to play with the toy, and timed how long they played with it Gender Time (secs) Same as ptt 192 331 275 341 280 310 Different from ppt 175 187 238 236 154 300

A psychologist was interested in finding out whether people with anorexia nervosa show higher levels of general anxiety than people without anorexia nervosa. She used a questionnaire to collect the following results Anxiety score Suffers from anorexia 84 89 91 78 65 77 82 76 84 Does not 59 suffer from anorexia 59 67 79 56 83 65 59 34