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8 How to read science

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Questions | Section 8: How to read science

Answers

1. What is the vertical axis on a graph called? What is the horizontal axis called? What does an axis measure?

A graph usually has a vertical axis (y-axis) and horizontal axis (x-axis). An axis measures data (information or results) or variables – and can measure anything. If time is one of the variables that is being compared, then this is always measured on the x-axis.

2. What is showing data on a graph called?

Showing data on a graph called is called plotting.

3. What does n stand for?

n is the mathematical term for number.

4. What is missing from this graph?

• a title
• units on the x-axis and y-axis
• a scale for the units on the x-axis and y-axis

5. Name two types of average

Mean average and median average.

6. What kind of distributions do these two 'data shapes' show?

Left: symmetrical, bell-shaped or 'normal' distribution. Right: positive skewness, common in laboratory data eg CD4 counts.

7. What kind of average would you use for data with (1) even distribution (2) uneven distribution? How would you show variation in the range of results for each of these?

If results are evenly distributed then the mean average is used. Even distribution is a term to describe data where most results are in the middle and a roughly similar number of results fall either side. It is also called a bell-shaped or 'normal' distribution. Variation is usually calculated using the standard deviation (usually 2 times standard deviation, which gives you the middle range of 95% of the results).

When the results are unevenly distributed (skewed) the median average is used. Variation is shown by giving the range of results (lowest and highest) or the Inter Quartile Range (middle half of the results).

8. Describe what happens to a drug when it is absorbed into the body.

When you take a drug, it is absorbed into the blood and distributed round the body. The drug reaches a peak level. Soon after this, the drug level falls steadily as its is eliminated from the body.

9. Explain the terms used on this graph: Cmax, Area Under the Curve, Tmax and T½.

• Cmax is the highest drug concentration reached after a dose.
• Area Under the Curve (AUC) is the total exposure to drug over the dosing period.
• Tmax is the time taken to get to the highest concentration.
• T½ is the time taken to reduce the highest concentration by half (by 50%) – a drug's 'half-life'. It takes approximately 5 half-lives for a drug to be cleared to negligible levels, but in theory, tiny quantities can be in the body for much longer.

10. What does Cmin stand for?

Cmin or Ctrough (trough level) is the lowest drug concentration just before the next dose.

11. What is the effect on drug levels of taking each dose of a drug on time?

Each dose taken on time makes sure that the drug stays above the lowest useful level.

12. Why is it important to keep drug levels in the body without these being too low or too high?

If drug levels are too low, then the drug will not be active enough to have any effect and there is a risk of resistance developing. If drug levels are too high, then the risk of some side effects is likely to be higher.

13. What is it important to remember about the way individual people process drugs and how does this affect drug levels?

• Some people will process the drug more quickly and get lower than average drug levels.
• Some people will process drugs more slowly and get higher than average levels.
• There can be differences in drug levels in the same person, even if the levels are measured at the same time after each dose – some drug levels are different 12 hours after a morning dose compared to 12 hours after an evening dose.

14. Explain what these units stand for and what are they typically used to measure in HIV infection:

• mm³
• mL
• log₁₀
• %

mm³ - cubic millimetre, CD4 counts

mL - millilitre, viral loads

log₁₀ - log value, (comparing different) viral loads

% - percentage, (comparing different) proportions from different samples, proportion of CD4 cells in white blood cell count (CD4%)

Questions | Section 8: How to read science

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