Statistical and Risk definitions
Incidence: The number of new cases of a disease that develop within a specified population over a specified period of time.
Prevalence: A proportion of a population that have the disease at a specific point in time.
Risk: risk is measured by looking at very large numbers of people, rather than at a particular individual. Risk is often presented in terms of Absolute Risk and Relative Risk.
- Absolute Risk (AR): is defined as the chance of a person developing a specific disease over a specified time-period. For example, a woman's lifetime absolute risk of breast cancer is one in nine. That is to say, one woman in every nine will develop breast cancer at some point in their lives. Absolute risk can also be expressed as a percentage (e.g. a woman's absolute risk of breast cancer can be written as 11 per cent instead of one in nine) or as a decimal (one in nine becomes 0.11).
- Relative Risk (RR): RR is used to compare risks associating with two variants or the risks of two different groups of people. For example, it can be used to compare a group of people with a certain genotype with another group having a different genotype. For a disease, a relative risk of 2 means that one group has twice the chance of developing a disease as the other group.
- Population Attributable Risk (PAR): PAR is different from AR. PAR estimates the proportion of disease in the study population that is attributable to a particular risk factor. For example, the PAR of a risk allele is the proportion of disease cases that would be eliminated if the disease risk for the carriers were to be reduced to that of non-carriers.
Genetic Risks from deCODEme.
- Risk relative to the population. Risk presented is usually the relative risk for a person, or a specific genotype of a person, compared to the population with matched gender and ethnicity. Risks of two individuals of the same gender and ethnicity could be compared in a simple manner. For example, if, compared to the population, the first individual has relative risk 1.5 and the second has relative risk 0.5, then the risk of the first individual compared to the second individual is 1.5/0.5 = 3.
- Variants and References. Only well established risk variants are used in deCODEme. The lists of relevant genetic variants will be constantly updated as more candidates meet the criterion. The published reference from which a relative risk estimate is calculated is provided. It is however important to note that a user might not find the exact relative risk number displayed in deCODEme in the corresponding reference. This is because, in most scientific publications, the relative risks, or odds-ratios, estimated are usually between two alleles or two genotypes. Since the average population risk can be expressed as a weighted average of the risks of different genotypes, using results from the reference, deCODEme performs the appropriate calculations to calculate the risk of a genotype group relative to the population, making it easier for the user to interpret the results.
- Modeling Genetic Risks. The calculations performed by deCODEme usually assume that the relative risks of different genetic variants multiply. This is a parsimonious model that usually fits the data of complex traits reasonably well. When judged to be well supported by data, more complex models will be implemented.
Allele: One of the variant forms of the DNA sequence at a particular locus, or location, on a chromosome. Different alleles can produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one). Other alleles may have no affect (are silent) but may tag genes or other nearby alleles that are causative or contribute to a genetic characteristic, such as a disease or disease susceptibility.
Genetic Scan: Analysis of the genome by typing it for multiple sequence variations. The deCODEme Genetic Scan measures over one million genomic locations with single nucleotide variations (SNPs).
Genome: All the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.
Genome Scan: Analysis of the genome by typing it for multiple sequence variations. The deCODEme Scan measures over one million genomic locations with single nucleotide variations (SNPs).
Genotype: The genetic makeup of an individual person. Used to refer to a specific sequence composition or alleles.