It is very important to put a time component into the equation, as every family's situation can change, until every member has had a test. Until an individual has received their test result, they have the option to move from the 'untested' group to the 'tested' group. This is a weakness in research counselling/testing protocols where a test is offered at a particular time, as other life factors such as deaths or marriages may have priority for the participants at that point in time. Also, an individual who has initially declined testing may be triggered to reconsider their decision by an outside event. It may be more revealing to consider the rate of uptake within each family, where AUf = An/N x Atime, and how this changes.
The way in which information is passed around the family now becomes relevant, as the starting point (t = 0) must be defined. A precise measure of the rate of uptake would be from the time that each individual became aware of the availability of a genetic test to the time when they made a decision to take the test. This shows the advantage of studies using the proactive approach, as this point can be defined, and the time taken to testing by each individual can be measured accurately.
The difficulties involved in measuring time delays without interfering in or prompting family communication routes make calculation of an exact figure for the time from being informed to having a test difficult. For example, it would be unlikely that patients could accurately recall when each and every family member was informed of the availability of a test. Without very specific records, it is impossible to establish whether significant delays in attending for testing are due to periods of reflection, or cancellations, or natural delays in referrals and clinic waiting times.
Defining t =0 as the date on which the first individual(s) in the family was informed that a mutation had been identified (the affected proband and/or previously known at-risk relatives) gives the most realistic starting point for a retrospective study or audit. However, it may be possible to record the time taken from the commencement of counselling at clinic for each individual.
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