Statistical tests for A2 biology

unit 6 exam

HideShow resource information

Chi squared test

  • Use when the measurements relate to sample size in different categories.
  • Produce a null hypothesis: There's no difference between the expected and observed results."
  • Calculate the value of chi and look at the tables. 
  • The degrees of freedom are one less than the number of categories.
  • If the value of chi is greater than the critical value we reject the null hypothesis and say there IS a significant difference between the observed and expected.
1 of 4

Spearman's rank correlation

  • Null hypothesis: there's no association between the two variables.
  • Calculate the Rs.
  • Look up on table the number of measurements and the critical values for each one
  • If your Rs is greater than the critical value you reject the null hypothesis.
2 of 4

Standard error

  • To find if there's difference between two means.
  • Null hypothesis: no difference between the no. of seeds in the dark than the ones at the sun.
  • Calculate standard error.
  • 95% confidence are 1.96+ mean and mean-1.96.
  • If these values don't overlap, there's a significant difference between the 2 variables. (Plot a whisker!!)
  • If they overlap we accept the null hypothesis.
3 of 4

T-test

  • Significant difference between two means.
  • Null hypothesis: There's no difference between the two variables.
  • Calculate t.
  • Degrees of freedom are both sample sizes -2.
  • Look up the degrees and critical values.
  • If t greater than critical, the null hypothesis is rejected.
4 of 4

Comments

Rogin Deylami

thank you, so helpful!

Lola

cool, what about the Man whitney U test? that would be fab! thanks!

Tilly - Team GR

Brilliant Thanks!

Similar Biology resources:

See all Biology resources »See all resources »