Cancer of the blood, including leukaemia and lymphoma, can be caused by mutations of stem cells in the bone marrow. A long-term study into the effects of radiation on the frequency of blood cancer was carried out on two groups of people: group 1 and group 2. These people were all born to mothers exposed to nuclear radiation during pregnancy. Table 2.1 summarises information about the two groups of people included in this study. Table 2.1 when born group 1 between 1948 and 1988 group 2 between 1950 and 1961 how the mothers were exposed to radiation working in a nuclear power plant and living in the town next to the nuclear power plant living next to a river contaminated by nuclear wastes from an accident at the same nuclear power plant time when mothers were exposed to radiation any time between January 1948 and December 1982 any time between January 1950 and December 1960 method of determining radiation exposure of mothers using badges worn by workers at the nuclear power plant to record their exposure to radiation from external radiation levels measured in the area individuals for whom blood cancer data were collected people who continued to live in the same town as the nuclear power plant people who continued to live in the area where they were born when blood cancer data were collected January 1948 until December 2009 January 1953 until December 2009 Until 2005, the data sources used for all of this information were paper based and obtained from hospitals, clinics and medical records. After 2005, data were collected electronically from databases at cancer clinics and from online death certificates. Table 2.2 shows some of the results from this study. Table 2.2 group 1 group 2 group 1 and group 2 combined number of people in the group studied 8466 11070 19536 male 4361 5588 9949 female 4105 5482 9587 outcomes up to December 31 2009 number of people not developing any cancer who were still alive 4053 5648 9701 number of people not developing any cancer who had died 898 1864 2762 number of people developing any cancer 220 288 508 number of deaths from any cancer 103 145 248 number of people developing blood cancer 32 26 58 number of deaths due to blood cancer 21 15 36 number of people where outcome not known 3295 3270 6565 The data were analysed to assess how the number of people who developed blood cancer was affected by their mothers' exposure to radiation during pregnancy. Fig. 2.1 shows the results of this analysis for the combined data from group 1 and group 2. Each plotted number includes all those people whose mothers' exposure to radiation during pregnancy was below, or up to, the exposure to radiation shown. [Figure 2.1]

1. (a)(i)In group 1, the proportion of people who were known to develop blood cancer out of all the people who were known to develop any cancer was 0.145. Calculate for group 2 the proportion of people who were known to develop blood cancer out of all the people who were known to develop any cancer. Give your answer to three decimal places.[1]
2. (a)(ii)It is possible to carry out a chi-squared test on the data in Table 2.2 to test whether there is a difference in the probability of individuals in group 1 and group 2 developing blood cancer. State one reason why the chi-squared test can be used with these data.[1]
3. (b)(i)Use Fig. 2.1 to describe the relationship between the number of people who developed blood cancer and their mothers' exposure to radiation during pregnancy.[3]
4. (b)(ii)Suggest an explanation for the relationship shown between the number of people who developed blood cancer and their mothers' exposure to radiation during pregnancy.[1]
5. (c)Evaluate the validity of the results of this study with reference to all the information provided.[3]
6. (d)Plant scientists were interested in the effect of radiation on the germination of seeds. They exposed seeds to the same intensity of radiation for different lengths of time and measured the proportion of seeds that germinated. Suggest three variables, other than intensity of radiation, that would need to be standardised in an investigation of this type.[3]

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