Correlation & Regression (Edexcel A Level Maths: Statistics): Exam Questions

Fred and Nadine are investigating whether there is a linear relationship between Daily Mean Pressure, hPa, and Daily Mean Air Temperature, °C, in Beijing using the 2015 data from the large data set.

Fred randomly selects one month from the data set and draws the scatter diagram in Figure 1 using the data from that month.

The scale has been left off the horizontal axis.

Describe the correlation shown in Figure 1.

Nadine chooses to use all of the data for Beijing from 2015 and draws the scatter diagram in Figure 2.

She uses the same scales as Fred.

Explain, in context, what Nadine can infer about the relationship between and using the information shown in Figure 2.

Using your knowledge of the large data set, state a value of for which interpolation can be used with Figure 2 to predict a value of .

Using your knowledge of the large data set, explain why it is not meaningful to look for a linear relationship between Daily Mean Wind Speed (Beaufort Conversion) and Daily Mean Air Temperature in Beijing in 2015.

A random sample of 15 days is taken from the large data set for Perth in June and July 1987.

The scatter diagram in Figure 1 displays the values of two of the variables for these 15 days.

Describe the correlation.

The variable on the -axis is Daily Mean Temperature measured in °C.

Using your knowledge of the large data set,

(i) suggest which variable is on the -axis,

(ii) state the units that are used in the large data set for this variable.

The table below shows data from the United States regarding annual per capita cheese consumption (in pounds) and the divorce rate (number of divorces per 1000 people) for ten years between 2000 and 2018:

Draw a scatter diagram to represent this data, with per capita cheese consumption on the horizontal axis and divorce rate on the vertical axis.

(i) Describe the correlation between per capita cheese consumption and divorce rate.

(ii) A newspaper reports the following statement:

"Eating more cheese reduces the chances of getting a divorce."

Comment on the validity of the statement.

Priya has been applying different voltages (, measured in volts) to an electrical circuit in her lab and recording the resulting currents (, measured in amps). The smallest voltage she applied was 0.5 volts, and the largest voltage she applied was 120 volts.

She found the equation of the regression line of on to be .

(i) Interpret the value 0.332 in this context.

(ii) Use the equation to predict the current for a voltage of 70 volts.

Explain why it would not be sensible to use the regression equation to work out:

(i) the current resulting from a voltage of 2000 volts

(ii) the voltage corresponding to a current of 20 amps.

The following table shows the height, cm, and weight, kg, for each of eleven students at a sixth form college.

The following statistics were calculated for the data on height:

mean cm, standard deviation cm

An outlier is an observation which lies more than 2 standard deviations from the mean.

(i) Show that is an outlier.

(ii) Explain why this outlier should be omitted from the data.

With the outlier data excluded, the equation of the regression line of on is .

(i) Exclude the outlier from the recorded measurements and draw a scatter diagram to represent the data for the remaining ten students.

(ii) Draw the regression line on your diagram.

The table below shows data from the large data set on the daily mean pressure, (hPa), and daily total sunshine, (hrs), in Camborne for a random sample of 12 days in 2015.

The equation of the regression line of on is .

Give an interpretation of the value of the gradient of the regression line.

Explain why it would not be reliable to use this regression equation to predict:

(i) the daily total sunshine on a day with a mean daily pressure of 980 hPa

(ii) the mean daily pressure on a day with 5.6 hours of total sunshine.

A maths teacher randomly selects 10 students from a class of 30 to answer a survey. The survey asks students how many practice questions they completed when revising for a recent test, , and their percentage score in that test, %. Summary statistics for are shown below.

, range of

The equation of the regression line of on is .

Explain which variable is the response variable.

Comment on the reliability of using the regression equation to:

(i) estimate the scores of the other students in the maths class,

(ii) estimate the scores of this cohort of students in a science class.

Ella measures how the extension, mm, of a thin piece of metal wire varies with the force applied to it, kN. She records her results in the table below.

Ella calculates the regression line of on to be .

Explain why this equation must be wrong.

The correct equation for the regression line of on is .

Interpret the value of 67.6 in this context.

Using the correct regression line, Ella estimates that if she applies a force of 1000 kN then the wire will show an extension of 14.7 mm. 

Give two reasons why Ella’s estimate may not be accurate.

A ride-sharing app collected data on the time, minutes, taken to complete a journey of distance, miles. Data from a random sample of 8 journeys is detailed in the table below.

By plotting a scatter diagram of on for this data, explain whether or not it is appropriate to use a linear regression model on this data.

Using a new random sample of thousands of journeys, the ride-sharing app calculated the regression line of time on distance to be .

The regression equation predicts that for journeys less than 0.3 miles the time taken will be less than zero minutes.  What is the most likely reason that the regression equation gives this false prediction?

An ice cream shop owner in Camborne is trying to use data from the large data set alongside their own past sales data to help them estimate future sales. The mean daily temperature per month, °C, is shown with the mean daily number of ice creams sold per month, , from 2015 in the table below.

The equation for the regression line of on is .

Find an estimate for the expected total number of ice creams sold in the month of July if the average daily temperature for that month is 14.9 °C.

Suggest one other variable from the large data set which could be used to improve this model.

The ice cream shop owner claims that there is a causal link between and , and so if the shop sells more ice cream, the month will be hotter. 

Comment on this claim.

The relationship between two variables and is modelled by the regression line with equation

The model is based on observations of the independent variable, , between 1 and 10.

Describe the correlation between and implied by this model.

Given that is measured in centimetres and is measured in days, state the units of the gradient of the regression line.

Using the model, calculate the change in over a 3‐day period.

Tisam uses this model to estimate the value of when .

Comment, giving a reason, on the reliability of this estimate.

The table below shows a comparison of the average house price, (£1 000), and the average yearly income, (£1 000), for different areas around the UK in 2021.

(i) Plot a scatter diagram of against , and

(ii) describe the correlation shown.

The equation of the regression line of on is calculated to be .

A news reporter uses this to claim that if you want a salary of £50 000, all you need to do is buy a house that costs £568 000.

Comment on the validity of the news reporter's claim.

Two researchers, Alwyn and Beth, are working on a project collecting data about the self-reported happiness of students on a scale from 0 to 10, , and the number of exams sat by those students, . After collecting data from 1000 students, they construct a scatter diagram and find the equation of the regression line of on to be .

Explain what correlation the data is likely to show in the scatter diagram.

What information about the original data set would need to be checked before using the regression line equation to estimate the self-reported happiness of a student sitting 8 exams?

After calculating the equation of the line of regression, Alwyn accidentally deletes all the data collected about the self-reported happiness scores.  Alwyn says it’s not a problem since he can use the regression line and the number of exams sat to recalculate all the values. Beth says that Alwyn is wrong and the original data is lost forever.

Explain which researcher is correct.

A consultant is trying to improve the efficiency of how a factory making chewing gum operates.  To help them do this, they collect many types of data about the factory workers.  One such type of data is the number of chewing gum packets made per shift.  The list below shows the number of chewing gum packets made by a particular worker (Worker 1) during the last 10 shifts worked.

Calculate the mean number of chewing gum packets made per shift by Worker 1 to the nearest whole number of packets.

The table below shows the mean number of chewing gum packets, , made by various workers along with how many hours of training, hours, they have received.

(i) Including your answer from (a), plot a scatter diagram of the data in the table above.

(ii) Given that the equation of the regression line of on is , add the regression line to your scatter diagram.

The consultant then goes on to collect even more data on other factory workers and records some of it in the table below.

Without adding this new data to your scatter diagram, what advice could the consultant give to the factory to improve the efficiency of their workers?

Paige takes a sample of 9 cities throughout the UK to compare the percentage of people living in a city who identify as vegan, %, and the percentage of restaurants offering vegan options in that same city, %.

The regression line of on is calculated, and it is used to predict values of for and . The values returned are and respectively.

Find the equation of the regression line of on .

In one of the cities, 1.16% of people were vegan and 55.9% of restaurants offered vegan options.

Use the equation of the regression line of on to estimate the percentage of restaurants offering vegan options in a city in which 1.16% of people are vegan. Give your estimated value of to 3 significant figures. Compare this to the information above.

Paige discovers that in one city every restaurant offers vegan options. Paige suggests that the equation of the regression line of on can be used to find the percentage of people in this city who identify as vegan. Explain why Paige is likely wrong.

An owner of a beach resort is comparing parasol sales, £, and sun cream sales, £, at the resort over a period of eleven days. The data is standardised by coding the variables using and . The values for the first ten days are plotted on the scatter diagram below.

On the eleventh day, the resort sold £246 worth of sun cream and £69 worth of parasols. Use this information to complete the scatter diagram.

The equation for the regression line of on is .

(i) Show that by using the regression line of on and the coding equations above, the regression line of on can be written in the form , where and are constants to be found to 3 significant figures.

(ii) Hence, or otherwise, find an estimate for the amount of parasol sales on a day where there are £170 of sun cream sales.