Hypothesis Testing (Binomial Distribution) (OCR AS Maths: Statistics)

A single observation is taken from a discrete random variable  to test  against . 

Using a 5% level of significance, find the critical region for this test.

The actual value for the observation was 10.

State a conclusion to the hypothesis test for this value, giving a reason for your answer.

Harry is using the random variable  to test the hypotheses:

Harry states that the critical regions are  and 

State, with a reason, the conclusion of Harry’s test given that a value of  is observed for the test statistic.

Sally is using the random variable  to test the hypotheses:

Sally observes the value  for her test statistic.

Calculate the -value of the observed test statistic .

Charlie, the owner of a chocolate shop, claims that more than 60% of people can tell the difference between two brands of chocolate.  Charlie takes a random sample of 150 customers and asks them to taste both brands of chocolate.  He records that 103 of them could successfully tell the difference between the two brands of chocolate.

State suitable null and alternative hypotheses to test Charlie’s claim.   

Test, at the 10% level of significance, whether Charlie’s claim is justified.

Nationally it is reported that four out of five people are right-handed.  Edward, an education researcher, takes a random sample of 30 children under the age of 18 years old and records the number of them, , who write with their right hand.

If the national proportion applies to the sample, write down a suitable distribution for .

Edward believes that the proportion of right-handed children differs from the national proportion for all people.  To test his belief, he uses his sample of 30 children.

State suitable null and alternative hypotheses to test Edward’s belief.

Using a 10% level of significance, find the critical values for a two-tailed test for Edwards’ belief. You should state the probability of rejection for each tail, which should be less than 0.05 for each.

Find the actual level of significance of a test based on your critical values.

Out of the 30 children in the sample, Edward recorded that 20 of them write with their right hand.

Comment on Edward’s belief based on this observation.

The existing treatment for a disease is known to be effective in 73% of cases.  Dr Sabir develops a new treatment which she claims is more effective than the existing one.  To test her claim she uses the new treatment on a sample of 60 patients with the disease and uses a binomial distribution to model the number of them who are cured.

Explain two assumptions that Dr Sabir has made when using a binomial distribution to model the number of patients cured by the vaccine.

Dr Sabir notes that her treatment was effective for 51 out of the 60 patients used in the sample.

Test, at the 1% level of significance, the validity of Dr Sabir’s claim that her treatment is more effective than the existing one. State your hypotheses clearly.

State the conclusion you would have reached if a 5% level of significance had been used for this test.

A “double yolker” is an egg which contains two yolks.  It is known that the probability of a chicken laying a double yolker is 0.1%.  A chicken farmer, Paolo, claims that double yolkers are rarer than the stated 0.1%.  To test his claim, Paolo records that his chickens lay 1217 eggs in a month and he uses these as his sample.  He discovers that none of these eggs are double yolkers.

Test, at the 5% level of significance, whether there is evidence to support Paolo’s claim that double yolkers are rarer than 0.1%. State your hypotheses clearly.

Paolo decides to take a larger sample so extends his test to three months.  During this time, a sample of 3425 eggs is formed and none of them are double yolkers.

Show that there is evidence, at the 5% level of significance, to support Paolo’s claim that double yolkers are rarer than 0.1%.

Paolo concludes that the probability of a double yolker is definitely less than 0.1%. Give a reason to explain whether Paolo’s conclusion is justified.

It is known that 61% of male dragons eat more than 20 sheep within a day.  Bill, a dragon breeder, suspects that the proportion of female dragons that eat more than 20 sheep within a day is different to males.

State suitable null and alternative hypotheses for a two-tailed test for Bill’s suspicion.

To test his suspicion, Bill observes a random sample of 80 female dragons during a full day and counts how many sheep they eat.  He finds that 40 out of the 80 female dragons ate more than 20 sheep within the day.

Test, at the 5% level, whether there is evidence to support Bill’s suspicion.

Determine the outcome of the test, at the 5% level, if Bill had used a one-tailed test to check whether the proportion of females eating more than 20 sheep within a day is lower than the proportion of males.

Historical records show that England wins 45% of Ashes test cricket series.  Rory believes that in the recent past that proportion has decreased.  To test this, he looks at their results in the last 17 series.

Using a 5% level of significance identify the critical region to enable Rory to test his claim.

England have won five series in the last 17. Use your answer in part (a) to state, with a reason, whether this sample supports Rory’s claim.

State an assumption made when using a binomial model.

It is known that there is a 0.35% chance of picking up a virus when downloading a file from a particular website.  After a security update, a security analyst believes that the chances of picking up a virus have been reduced.  In a sample of 1542 files downloaded from the website, 1 virus is detected.  The analyst wishes to use a hypothesis test with significance levels  appropriately chosen to allow her to report with as much certainty as possible that her belief is correct.

Test at the 1%, 5% and 10% significance levels and explain which of those significance levels the analyst should use for the test in her report.

At a school it is known that 80% of students obtain 3 or more A* to C grades in their A levels.  The principal claims that another local school has a different proportion of A* to C grades at A level.

Last year the other school had 57 out of 80 students achieve 3 or more A* to C grades at A level.

Using a two-tailed hypothesis test, test the principal’s claim at the 5% significance level stating suitable null and alternative hypotheses.

Suggest a hypothesis test with an alternative significance level that would lead to a different conclusion.

On a particular Pokémon game, it is possible to create offspring through breeding.  Sometimes when two Pokémon are bred together, their offspring possess a hidden ability.

One Pokémon fan website,, claims that the probability of producing offspring with a hidden ability is 0.6.  Another website,, claims the probability is higher.

Maya conducts an experiment and finds that 38 out of 50 of her Pokémon’s offspring possess a hidden ability.

Use Maya’s sample to test the claim of website   against website  at the 5% significance level, stating your null and alternative hypotheses clearly.

Website  claims that the probability is 0.8.

Using a two-tailed hypothesis test, test the claim at the 5% significance level and make a statement about which website is more likely to be correct.

The critical regions of a two-tailed hypothesis test to test ’s claim are and . Find the actual level of significance.

A single observation is taken from a discrete random variable to test the hypotheses

where   is a positive integer to be found.

Given that at the 10% significance level one of the critical regions is , find the value of .

Find the other critical region for the test at the 10% significance level.

It is known that customers have an 83% success rate when attempting to order bundles of 5 or more festival tickets from a particular website.  A second website claims that its customers have a greater probability of success.

State suitable null and alternative hypotheses to test the second website’s claim.

In one day, 1159 out of 1358 bundles of 5 or more tickets are successfully ordered from the second website.

Test the second website’s claim using a 1% significance level.

It is suggested that instead of using a 1% significance level for the test, the critical region could have been used for testing the second website’s claim against observed data for the number of successes out of 1358 attempted orders. 

Find the probability of incorrectly rejecting the null hypothesis if that critical region is used.

The table below shows information for England, taken from the 2011 census.

 
Chase, an anthropologist, was studying the proportions of elderly people (aged 65 or over) in different countries in 2011. He claimed that there was a higher proportion of elderly people in England compared to the USA. Chase took a random sample of 1000 people in the USA and recorded that 152 of them were elderly.

Monica, a student, wants to use the sample to test Chase's claim but she cannot decide which one of the following is the better null hypothesis to use:

.

Using your hypotheses from part (a)(ii), test Chase's claim using a 10% level of significance. Give your conclusion in the context of the question.

Monica removes 100 people from Chase's sample as they did not live in the USA, they were there on holiday. None of these 100 people were elderly.

State, with a reason, whether this information will change the outcome of the hypothesis test in part (b).

A single observation, , is taken from a discrete random variable to test  against    

For the purposes of this test, the critical regions are specified as being   and .

Calculate the probability of incorrectly rejecting the null hypothesis when conducting this test.

The probability of a wild Asian elephant living past 40 years old is 45%. 

Rosie, a zoologist, obtains data on 25 elephants in captivity and records their ages at death. She suspects that the proportion of Asian elephants that live past 40 years old is smaller for those in captivity than those in the wild.

Using a 1% level of significance, find the critical value of a one-tailed hypothesis test to enable Rosie to test her suspicion. Clearly state your hypotheses.

Rosie finds that only one elephant, out of the 25 in captivity, lived past 40 years old. 

A newspaper article claims that 60% of animal species have become extinct since 1970.  Iggy, a taxonomic biologist, has been studying animal extinction statistics and believes that the proportion is different to the newspaper’s claim.

Iggy collects a random sample of 500 species that were recorded as being in existence in 1970 and records the number that are now extinct.  He uses multiple sources to verify the species’ taxonomic status and finds that the number of extinct species could be as low as 319 or as high as 329.

Iggy wants to use his findings to test his belief, but he also wants to make sure that the test will support his belief for all possible values of the number of extinct species. What is the smallest possible integer percentage value he could use for a significance level to make sure that the test supports his belief?

Iggy repeats this process with a different random sample of 1000 species for which the taxonomic status is more certain, and in this second sample he finds the total number of extinct species to be 650.

Show that the evidence from this second sample offers better support for Iggy’s hypothesis than the evidence from his first sample.

Historic company data shows that the proportion of customers ordering a large vegetable box from Lakebridge Organics is 0.4.

Last week a random sample of 35 customers’ orders was taken and it was found that 21 of them had ordered a large vegetable box.

Test, at the 5% significance level, whether this suggests that the proportion of customers ordering large vegetable boxes has increased. State your hypotheses clearly.

Historic company data shows that the proportion of customers ordering a medium vegetable box is also 0.4.  Lucinda, a delivery driver, suspects that the proportion of current customers ordering medium boxes is different from 0.4.  She takes a random sample of 40 customers’ orders.

A football team, Dinamo Galacticos, are trying to decide on a colour for their new kit.  They are told by a local sports commentator that the proportion of games won by teams wearing red is 0.5.

The manager takes a random sample of 20 games where one team wears red and finds that  of them are won by the team in red.  Assuming that the proportion of games won by teams in red really is 0.5, then the probability that n or fewer games out of 20 would be won is equal to 0.1316 correct to 4 decimal places.

Find the value of .

The manager decides to increase her random sample to include 50 games.  She suspects that the actual proportion of games won by teams in red is lower than 0.5.

The sports commentator later says that he may have gotten mixed up, and that he thinks it is actually teams wearing green that win 50% of their games.

Given that teams wearing green have won 12 games from the last 35 in which they played, test at the 5% significance level whether the commentator’s new claim is justified. You must clearly state your null and alternative hypotheses.

A catering company’s past records show that the proportion of their customers who are vegetarian has previously been 0.2.  The company decides to take a random sample of 30 current customers to test whether that figure 0.2 is still valid for their current customer base.

Let  denote the number of vegetarians in the sample. Find the critical region for a two-tailed test using a 10% significance level, stating the actual probability in each tail.

The number of vegetarian customers in the sample is 11.  One of the company’s employees used the same sample to suggest that this shows that the proportion of vegetarian customers has not just changed but has in fact increased.

Use this test statistic to test, at the 5% level of significance, whether the proportion of vegetarian customers has increased. State your hypotheses clearly.

A random variable has distribution  .

In order to test the hypotheses

a random observation of  is taken and found to be 5.

Carry out a hypothesis test at the 10% significance level.

Another random variable has distribution  .

A random observation of is taken and found to be 1. Using the same hypotheses as above, find the maximum value of  for which  would not be rejected at the 10% significance level.

Another random observation of  is taken and found to be .  For the same hypotheses as above, this provides evidence to reject  at the 5% significance level. 

Using your answer to part (b) as the value for , find the possible values of .