An environmental scientist investigates whether a new filtration system reduces microplastic concentration in local water sources. Water samples from several locations are tested before and after the installation of the filtration system. The changes in microplastics are recorded in Table 1.

Table 1: Direction of change in microplastic concentration

Change Category	Decreased microplastics ( $+$ )	Increased microplastics ( $-$ )	No change (0)
Number of locations	29	13	5

Use the data in Table 1 to calculate the value of the test statistic $S\,$ for a sign test. Explain how you obtained your answer.

Table 1: Direction of change in microplastic concentration

Change Category	Decreased microplastics ( $+$ )	Increased microplastics ( $-$ )	No change (0)
Number of locations	29	13	5

Use the data in Table 1 to calculate the value of the test statistic $S\,$ for a sign test. Explain how you obtained your answer.

Inferential testing (A-level only)

Question 17

Table 1: Direction of change in microplastic concentration

Markscheme

Inferential testing (A-level only)

Question 17

Table 1: Direction of change in microplastic concentration

Markscheme

Inferential testing (A-level only)

Question 17

Table 1: Direction of change in microplastic concentration

Inferential testing (A-level only) Questions

Inferential testing (A-level only)

Question 17

Table 1: Direction of change in microplastic concentration

Inferential testing (A-level only) Questions