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Design and Data Analysis in Psychology I

Design and Data Analysis in Psychology I. School of Psychology Dpt. Experimental Psychology. Salvador Chacón Moscoso Susana Sanduvete Chaves. Relationships between two qualitative variables. Lesson 10. 1. Chi square test. When samples are independent.

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Design and Data Analysis in Psychology I

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  1. Design and Data Analysis in Psychology I School of PsychologyDpt. Experimental Psychology Salvador Chacón Moscoso Susana Sanduvete Chaves

  2. Relationships between two qualitative variables Lesson 10

  3. 1. Chi square test • When samples are independent. • When both variables are nominal (although they also could be ordinal). • Assumptions: • N > 20 • Expected value for each cell (E) ≥ 5 (in tables 2x2) • E ≥ 5 in at least 20% of cells (in tables higher than 2x2) • When assumptions are violated, Fisher Exact test can be used (section 2).

  4. 1. Chi square test

  5. 1. Chi square test. Example A middle-school teacher was interested in determining if there was a relationship between math anxiety and gender among students at her school. The confidence level (CL) is 95%. The results are presented in the contingency table below.

  6. 1. Chi square test. Example *Expected value into brackets

  7. 1. Chi square test. Example The null hypothesis is rejected. There is relationship between math anxiety and gender.

  8. 2. The Fisher Exact test • When samples are independent. • When both variables are nominal. • When both variables are dichotomous. • When Χ2assumptions are violated.

  9. 2. The Fisher Exact test

  10. 2. The Fisher Exact test. Example We would like to test if an anxiety reduction program is effective to eliminate the post-intervention fear. The confidence level (CL) is 95%. The results are presented in the contingency table below.

  11. 2. The Fisher Exact test. Example Z=2.25 > Zα/2=1.96: The null hypothesis is rejected. The anxiety reduction program is effective to eliminate the post-intervention fear.

  12. 3.The McNemar test • When samples are dependent. • When both variables are nominal. • When both variables are dichotomous.

  13. 3.The McNemar test. Example A psychologist wanted to study if, the first day in the kindergarten, children started relationships mainly with adults, and after 6 months, mainly with other children (CL=95%).

  14. 3.The McNemar test. Example The null hypothesis is rejected. Firstly, children in the kindergarten interact more with adults; in 6 months, with other children.

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