Chi-squared Test

• Use this test when: the measurements relate to the number of individuals in particular categories and the observed number can be compared with an expected number, which is calculated from a theory
• Compares observed with theoretical expected results; calculation generates a X^2 value, the higher, the greater the difference between observed and expected (null hypothesis: no statistical difference between observed and expected)
• Calculate the expected value; may be mean of the expected values or if in inheritance, you add expected values and apply ratio; the find degrees of freedom (n-1) and compare to critical value
• Chi-squared test Formula:

  A) observed value

  B) expected value

  C) expected value

  
• To claim biological reason caused difference; biologists only accept 95% confidence, if under results difference occurred due to chance; if number exceeds critical at 0.05 level, you can reject the null hypothesis, but if X^2 value is less, you accept the null hypothesis