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Answers to these exercises can be found in Part 4, at the end of the chapters.

1 1.9.1 Rounding and significant digitsRound the following numbers to two decimal places. Use the rules plus common sense.12.2345144.567373.66513.665299.4545Round the same numbers to three significant digits.

2 1.9.2 Interpreting data: does screening save lives?62 000 women in a health insurance scheme were randomly allocated to either a screening programme for breast cancer, or no screening. After 5 years, the following results were observed (Table 1.4):Does screening save lives? Which numbers tell you so?Among the women in the screening group, the death rate from all other causes in the ‘Refused’ group was almost twice that in the ‘Examined’ group. Did screening cut the death rate in half? Explain briefly.Was the study blind?

3 1.9.3 Hypothesis and null hypothesisIn a study designed to assess whether undernutrition is a cause of short stature in poor inner‐city children:State the hypothesis (H1)State the null hypothesis (H0)Consider:confounding factorssources of systematic biasConsider ways to minimize the effects of confounding and systematic bias