Chi-squared test

Question 1

What is the chi-squared test?

Answer 1

• stastical test that measures the size of the difference between the results you actually get and those you expected to get

Question 2

WHy is the chi-squared test important

Answer 2

• helps you determine whether differences in the expected and observed results are significant or not
• by comparing the sizes of the differences and the number of observations

Question 3

What is the chi-squared test used for?

Answer 3

• conventionally used to test the null hypothesis

Question 4

What is the null hypothesis?

Answer 4

• the null hypothesis is that there is no significant difference between what we expect and what we observe
• any differences we see are due to chance

Question 5

What do the values of the test show?

Answer 5

• find the probability of the difference beting due to chance alone

Question 6

What does a large test result mean?

Answer 6

• large chi-squared values mean there is a statistically significant difference between the observed and expected results
• and the probability that these differences are due to chance is low
• there must be a reason, other than chance, for the unexpected results

Question 7

What affects the size of the chi-squared value calculated?

Answer 7

• the number of categories being compared in an investigation

Question 8

What are degrees of freedom?

Answer 8

• degrees of freedom is the number of comparisons being made
• calculated as n-1
  
  • where n is the number of categories or possible outcomes (phenotypes in the case of phenotypic ratios) present in the analysis

Question 9

What is the critical value in the probability table?

Answer 9

5% (p=0.05)

Question 10

what if the value found is less than the critical value?

Answer 10

• then we do not have sufficiently strong evidence to reject the null hypothesis
• accept the null hypothesis
  
  • there is no significant difference between what we observed and what we expect