An Investigation into Childhood Leukaemia in Northampton

Glossary

age-standardised rates - because diseases occur at different rates in different age-groups it is sometimes difficult to meaningfully compare the rates in two populations that have different age structures (since these populations could, for instance, have very different rates simply due to the fact that people in the populations have different ages).  To get round this we calculate age-standardised rates that takes into account the age structure of a population so that rates can be compared. 

anaemia occurs when a person does not have enough red blood cells or haemoglobin (the molecule in red blood cells) to carry sufficient oxygen around the body 

ALL acute lymphoblastic leukaemia.  There is more than one type of white blood cell.  Leukaemia is classified by the type of white blood cell is produced in excess. ALL and CML are different because they involve the over-production of different sorts of immature white blood cell. 

artefact an artificial product, something that did not exist until produced or introduced by the process of observation 

benzene is a naturally occurring substance produced by volcanoes and forest fires and present in many plants and animals.  It is also a major industrial chemical made from coal and oil.  As a pure chemical, benzene is a clear, colourless liquid.  It is used to make other chemicals, some types of plastic, detergents, and pesticides.  It is also in a component of petrol.  Benzene is an aromatic hydrocarbon molecule 

case definition the criteria that an epidemiologist sets to identify patients that will be considered as "cases" in an epidemiological study (this is not necessarily the same as what a doctor would consider as a "case") 

case-control study is an epidemiological study in which people with a disease are compared to a similar group of people without the disease to see if there are any differences in their exposure to agents that are thought to be possible causes of the disease 

carcinogen is something that causes cancer, e.g. benzene is known to be a carcinogen 

chromosomes are rod-shaped structures in the nucleus of cells that contain the genes or hereditary information 

cluster is a number of things or events of the same kind occurring or situated close together.   Cases of a disease can aggregate together either in time or place or both.  This last group are called space-time clusters. Diseases can cluster because of some shared cause or risk factor or because of the natural history of the disease or can be due to chance 

CML chronic myeloid leukaemia. See ALL above. 

cytotoxic drugs are drugs that kill cancer cells 

DNA deoxyribonucleic acid is a molecule which controls the structure and function of the cells that make up the human body.  It is found in the chromosomes in the nucleus.  Most radiation damage to cells is thought to involve changes to the DNA.  These changes are known as transformations. The effects of cell transformation may take may years to appear. 

Down's syndrome occurs when a person is born with an extra chromosome (chromosome 21).  People with Down's syndrome have some degree of mental impairment.  They are also more likely to suffer from a number of other illnesses including leukaemia and heart problems 

effective dose an equivalent dose of radiation weighted for the susceptibility to harm of different tissues 

electron an elementary particle with very low mass and a negative charge 

epidemiology is the study of the frequency and patterns of disease in groups of people 

equivalent dose  the absorbed dose of radiation weighted for the harmfulness of different types of radiation 

free radical a grouping of atoms with an unpaired electron which makes it very chemically reactive 

germ cells these are the cells in the body that carry the genetic information necessary for sexual reproduction.  Sperm and ova are germ cells. 

hazard anything which may cause danger 

high-LET radiation is the radiation characteristic of heavy charged particles such as protons and alpha 
particles where the distance between ionising events is small 

ICD the International Classification of Diseases is a system of agreed codes for classifying illnesses to help in analysing data and comparing different groups and places 

incidence is the number of new cases of a disease that occur in a specified period of time (e.g. one year) 

in utero in the womb, that is to say, before birth 

ionising radiation "radiation" is a very broad term and includes visible light, ultraviolet rays, radiowaves, x-rays etc.  When people worry about radiation they usually mean ionising radiation.  Ionising radiation is electromagnetic or particulate radiation that can cause ionisation (the ejection of an electron from an atom).   When materials emit ionising radiation they are said to be radioactive (cf.  radioactivity) 

ionisation the process of forming ions from neutral atoms 

LET linear energy transfer - the average amount of energy lost per unit track length 

leukaemia is a form of cancer, it occurs when the body makes too many immature white blood cells 

low-LET radiation is radiation such as X-rays or gamma rays where the distance between ionising events is large 

lymphoma any cancer of the lymphoid tissue 

multifactorial this term means that a disease (or other outcome of interest) may have more than one cause, so that a combination of causes (or alternative combinations of causes) are required  to produce it 

radioactive decay is the process whereby radioactive substances break down into other substances 

radioactivity describes the property of some materials to emit ionising radiation.  Radioactive materials have atomic nuclei that are unstable and change or decay into different more stable nuclei, giving out ionising radiation as they do so. 

relative risk (RR) compares the incidence of a disease in a group with a possible risk factor with the incidence of the disease in a group who do not have this risk factor.  If the relative risk is 1 then there is no difference in how often the disease occurs in the two groups.  If the relative risk is more than 1 then the disease is more likely to occur in the group with the risk factor than the group without the risk factor.  If the relative risk is less than 1 then the disease is more common in the group without the "risk factor" than in the group with it.  The relative risk tells you how many times more common the disease is in the group with the risk factor e.g. a relative risk of 2 means it is twice as likely, a relative risk of 20 means that it is 20 times as likely and a relative risk of 0.5 means that it is half as likely 

risk the probability or chance that some event will happen (usually injury, harm or damage) 

statistical significance in order to decide how to interpret the results of a study we can apply statistical tests to them.  These tests estimate how likely we are to see the observed (or a more extreme) result if we assume there is no real difference between what we are looking at and what we are comparing it to.  If the test shows that we are unlikely to see the result we got (e.g. that it would only happen 1 in 20 or 1 in 100 times) then way say that it is "statistically significant". We need to specify what level of chance we are considering as unlikely.  (Just because something is very unlikely, i.e. very "statistically significant",  it does not necessarily mean that it is very important!). 

toxin a poisonous substance from an animal or plant.