Binomial Hypothesis Testing (DP IB Applications & Interpretation (AI)): Revision Note

Binomial hypothesis testing

What is a hypothesis test using a binomial distribution?

• You can use a binomial distribution to test whether the proportion of a population with a specified characteristic has increased or decreased

  • These tests will always be one-tailed

  • You will not be expected to perform a two-tailed hypothesis test with the binomial distribution

• A sample will be taken and the test statistic x will be the number of members with the characteristic, which will be tested using the distribution 

  • This can be thought of as the number of successes

What are the steps for a hypothesis test of a binomial proportion?

• STEP 1
  Write the hypotheses

  • H₀ : p = p₀

    • Clearly state that p represents the population proportion

    • p₀ is the assumed population proportion

  • H₁ : p < p₀ or H₁ : p > p₀

• STEP 2
  Calculate the p-value or find the critical region

  • See below

• STEP 3
  Decide whether there is evidence to reject the null hypothesis

  • If the p-value < significance level then reject H₀

  • If the test statistic is in the critical region then reject H₀

• STEP 4
  Write your conclusion

  • If you reject H₀­ then there is evidence to suggest that...

    • The population proportion has decreased (for H₁ : p < p₀)

    • The population proportion has increased (for H₁ :  p > p₀)

  • If you accept H­₀ then there is insufficient evidence to reject the null hypothesis which suggests that...

    • The population proportion has not decreased (for H₁ : p < p₀)

    • The population proportion has not increased (for H₁ : p > p₀)

How do I calculate the p-value?

• The p-value is determined by the test statistic x

• The p-value is the probability that ‘a value being at least as extreme as the test statistic’ would occur if null hypothesis were true

  • For H₁ : p < p₀ the p-value is 

  • For H₁ : p > p₀ the p-value is 

How do I find the critical value and critical region?

• The critical value and critical region are determined by the significance level α%

• Your calculator might have an inverse binomial function that works just like the inverse normal function

  • You need to use this value to find the critical value

  • The value given by the inverse binomial function is normally one away from the actual critical value

• For H₁ : p < p₀ the critical region is  where c is the critical value

  • c is the largest integer such that 

    • Check that 

• For H₁ : p > p₀ the critical region is  where c is the critical value

  • c is the smallest integer such that 

    • Check that