The present invention relates to a method for quantifying stress in a user, wherein said method allows establishing discrimination between stressed users and relaxed users. The invention is characterized by the use of stress patterns based on sigmoid transfer functions to allow quantifying stress in a larger number of situations.
1. A method for quantifying stress in a user which comprises the following steps: • obtaining a stress pattern for the user which in turn comprises: o a mean heart rate value (hµr ) and a heart rate variance value (hσr ) corresponding to a relaxed state of the user, o a mean heart rate value (hµs ) and a heart rate variance value (hσs ) corresponding to a stressed state of the user, o a mean galvanic skin response value (gµr ) and a galvanic skin response variance value (gσr ) corresponding to a relaxed state of the user, o a mean galvanic skin response value (gµs ) and a galvanic skin response variance value (gσs ) corresponding to a stressed state of the user, • measuring the heart rate (hµ ) and the galvanic skin response (gµ ) of the user in whom stress is to be quantified, • obtaining at least one rule for the relaxed state of the user which comprises: o defining a decreasing function in an interval [a, b] of real values which can be expressed as: f H r h h μr h σr = 1 - 1 1 + exp - h - h μr h σr <img class="EMIRef" id="131193636-ib0013" /> o defining a decreasing function in the interval [a, b] which can be expressed as: f G r g g μr g σr = 1 - 1 1 + exp - g - g μr g σr <img class="EMIRef" id="131193636-ib0014" /> o defining a decreasing basis function in the interval [a, b] which can be expressed as: Brbbμrbσr=1-11+exp-b-bμrbσr for predetermined values bµr and bσr , • obtaining at least one rule for the stressed state of the user which comprises: o defining an increasing function in the interval [a, b] which can be expressed as: f H s h h μs h σs = 1 1 + exp - h - h μs h σs <img class="EMIRef" id="131193636-ib0016" /> o defining an increasing function in the interval [a, b] which can be expressed as: f G s g g μs g σs = 1 1 + exp - g - g μs g σs <img class="EMIRef" id="131193636-ib0017" /> o defining an increasing basis function in the interval [a, b] which can be expressed as: Bsbbμsbσs=11+exp-b-bμsbσs for predetermined values bµs and bσs , • determining the value of the function fHr and fGr for the heart rate (hµ ) and galvanic skin response (gµ ) values measured on the user and determining the minimum m r = min f H r , f G r <img class="EMIRef" id="131193636-ib0019" /> • determining the value of function fHs and fGs for the heart rate (hµ ) and galvanic skin response (gµ ) values measured on the user and determining the minimum ms = min{fHs, fGs} • defining the weight function Pr(x) = min{mr, Br(x, bµr , bσr )} for any value of x in the interval [a, b], • defining the weight function Ps(x) = min{ms, Bs(x, bµs , bσs )} for any value of x in the interval [a, b], • defining the result function P(x) = max{Pr(x), Ps(x)} for any value of x in the interval [a, b], • obtaining a centralization measurement of the function P(x) in the interval [a, b] as a stress quantification value in the user. 2. The method according to claim 1, characterized in that the interval [a, b] is the interval [0,1]. 3. The method according to claim 2, characterized in that bµr , bσr , bµs , bσs take the value 1. 4. The method according to claim 1, characterized in that it additionally incorporates: • one or more rules corresponding to the relaxed state, to the stressed state or rules for both states, wherein: o if the rule corresponds to the relaxed state, said rule has a decreasing sigmoid function for the heart rate, a decreasing sigmoid function for the galvanic skin response and a decreasing sigmoid basis function, o if the rule corresponds to the stressed state, said rule has an increasing sigmoid function for the heart rate, an increasing sigmoid function for the galvanic skin response and an increasing sigmoid basis function, • the minimum of the sigmoid function corresponding to the heart rate value (hµ ) and of the sigmoid function corresponding to the galvanic skin response value (gµ ) respectively measured on the user are determined for every defined rule, • determining the weight function for every technical rule as the minimum function between the previous minimum value and the basis function of the technical rule; and, • the result function P(x) is assessed as the maximum of both the weight functions of the rule for the relaxed state and the rule for the stressed state and the weight functions of the additional rules. • providing the centralization measurement of the weight function obtained in the previous step in interval [a, b] as a stress quantification value in the user 5. The method according to claim 1, characterized in that the measurement of the heart rate (hµ ) and the measurement of the galvanic skin response (gµ ) of the user are carried out by calculating the arithmetic mean on a set of samples taken over a time period. 6. A method for determining a stress pattern, characterized in that: • for each of the states, the relaxed state and the stressed state, a sampling of m samples is carried out over time in instants ti, wherein i = 1...m, both of the heart rate (h) and of the measurement of the galvanic skin response (g) of the user, • a subset of n consecutive samples is taken comprising the sample taken in the instant tm and the previous consecutive samples wherein n < m, • the arithmetic mean is evaluated on the subset of n samples for obtaining the measurements both of the heart rate (hµ ) and of the galvanic skin response (gµ ) of the user, • the variance is evaluated on the subset of n samples for obtaining the measures of dispersion both of the heart rate (hσ ) and of the galvanic skin response (gσ ) of the user, • the evolution of the quantification of the stress is assessed by taking as consecutive measurements both of the heart rate (hµ ,hσ ) and of the galvanic skin response (gµ ,gσ ) of the user those which result from calculating the arithmetic mean on the subset of samples which results from gradually adding to the subset of n samples a specific number of samples obtained in the following instants of time and in turn discarding the same number of older measurements. 7. A method for determining a stress pattern for an individual, characterized in that: a) a number of users in whom a test is carried out for determining the individual's response to stress by determining one or more numerical factors characterizing it is taken, b) empirically determining the stress pattern for each individual, c) carrying out a clustering process determining a number of "typical" patterns representative of each group resulting from the clustering, d) for the individual, subjecting him to the test used in step a) and finding the closest numerical factors corresponding to the groups obtained in the clustering according to the Euclidean measure and pre-assigning the pattern of the closest group to the individual. 8. A device for quantifying stress in a user comprising: • a first sensor for detecting the heart rate signal, • a second sensor for detecting the galvanic skin response signal, • a central processing unit in communication with the first and second sensor adapted for carrying out a method according to any of claims 1 to 7, • an output in communication with the central processing unit for obtaining the stress quantification value.