Statistics

Question 1

2 marks

The inheritance of body colour in fruit flies was investigated. Two fruit flies with grey bodies were crossed. Of the offspring, 152 had grey bodies and 48 had black bodies.
Explain why a statistical test should be applied to the data obtained in this investigation.

Answer 1

So that you can determine the probability, that the differences are due to chance

Question 2

2 marks

The doctors carried out a statistical test to determine whether the antibody concentrations were significantly different in girls given two doses of the vaccine, compared with those given three doses. They determined the mean concentrations of antibody 9 months after the first dose of vaccine.
What statistical test should the doctors have used? Give the reason for your choice

Answer 2

1. Student t-test
2. Comparison of 2 means

Question 3

2 marks

Scientists investigated the frequency of daisies in trampled and non-trampled sites
What statistical test should the scientists use.

Answer 3

1. Chi- squared test
2. Comparing frequency of categorical data

Question 4

2 marks

Littorina littorea is a species of snail found on rocky sea shores.A student investigated variation in snail shell height in two populations of snails.
The student noticed there was a difference in shell height between these populations of snails. He wanted to investigate if the difference was significant.
Give a suitable null hypothesis to use in his investigation and name the statistical test to use with these data.

Answer 4

1. The difference in populations doesnt affect shell heights
2. Student t-test

Question 5

3 marks

x2 was calculated. When this value was looked up in a table, it was found to correspond to a probability of less than 0.05. What conclusion can you draw from this?

Answer 5

1. Less than 5% probability that differences are due to chance
2. Reject null hypothesis
3. Differences are significant

Question 6

3 marks

The scientists used a statistical test to test the following null hypothesis:
‘The presence of KIR2DS1 in the mother’s genome does not affect the frequency of births above 4500 g’
The scientists calculated a P value of 0.03 when testing their null hypothesis.
What can you conclude from this result? Explain your answer

Answer 6

1. Less than 5% probability that differences are due to chance
2. Reject null hypothesis
3. Differences are significant
4. The presence of KIR2DS1 in the mother’s genome does affect the frequency of births above 4500 g

Question 7

2 marks

The scientists tested their null hypothesis using the chi-squared statistical test.
After 1 cycle their calculated chi-squared value was 350
The critical value at P=0.05 is 3.841
What does this result suggest about the difference between the observed and expected results and what can the scientists therefore conclude?

Answer 7

1. PDC There is a 5% probability that the difference (between o and e) are due to chance
2. Null hypothesis rejected
3. Differences are significant
4. The number of cycle does affect the number of plants

Question 8

When to use spearmans rank

Answer 8

Looking for correlation between two variables

Question 9

uncertainty formula

Answer 9

resolution/2

Question 10

uncertainty for repeated readings

Answer 10

range/2

Question 11

Explain uncertainties

Answer 11

• Always add % uncertainties if you are multiplying or dividing numbers with uncertainties
• Always add absolute uncertainties if you are adding/ subtracting numbers with uncertainties e.g. when measuring length of image= 2 uncertainties in start and end point

Question 12

How to work out % error

Answer 12

(uncertainty/measured value) x 100