Changes in reaction time of clot assays are usually expressed only in time units, which fails to indicate the extent of the increase or decrease of the reaction time of the tested specimens against that of the basic sample. Reaction time increases of, e.g. , 6 seconds in tested samples, compared to basic sample reaction times of 12 and 24 seconds respectively, signify an increase twice as large in the first as in the second instance.Changes in reaction time of clot assays can be expressed as the increment or decrement of the reaction time per time unit. This amount of increase or decrease (positive or negative alteration of reaction time, T
a
) can be expressed as the quotient of the difference between the reaction times of the tested (T
x
) and basic (To) samples and of the basic sample, e.g. in seconds per second, T
a
=T
x
-To/To. A test sample reaction time 6 seconds longer than basic sample reaction times of 12 and 2k seconds would mean an increase of 0.5 and 0.25 seconds per second, respectively.Reaction time changes of tested samples against that of the standard sample (T
std
) can be calculated in a similar way, T
a
=T
x
-T
std
/T
std
.It can be assumed that this parameter reflects the intensity of the increase or decrease of reaction time per time unit. The quotient of the tested and basic samples can be considered as the coefficient of the increase or decrease of the total reaction time (CT=T
x
/To).