A-Level Edexcel Biology Statistical Tests

Review A-Level Edexcel Biology statistical tests through the available evidence on using correlation coefficients to judge relationship strength.

Exam points

describe how a correlation coefficient tests relationship strength against critical values

[Maximum number: 3]

Mycobacterium tuberculosis (Mtb) and human immunodeficiency virus (HIV) are two pathogens that infect people. When people infected with either pathogen become infected with the other pathogen the disease is worse.

The graph shows the number of people who have TB and the percentage of the population who have HIV. Each plotted point represents data from a different country. Number of people who have TB per 100000 population

Figure for Question A.1.9—Statistical tests question 1 — Edexcel A-Level Biology A2

Describe how the strength of the relationship between the number of people who have TB and the percentage of people who have HIV could be determined.

A description that includes three of the following points:

- correlation (coefficient) test / named (correlation) test (1)

- \{coefficient / rho / $\left.r / r_{\mathrm{s}} / \rho\right\}$ value calculated (1)

- closer (r) value is to $\{1 /-1\}$ the stronger the correlation (1)

e.g. Pearson, Spearman DO NOT ACCEPT incorrect named test e.g. T test, Z test, MWU, chi squared

ACCEPT compare r value to critical values at (less than) $\{0.05 / 5 \%\}$ sig levels

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A.1.9—Statistical tests question 1