A method for estimating respiratory rate, wherein the method comprises steps of: - gathering data related to a pulse wave in an electrical form, - extracting a beat series with noise removal and interpolated beats for missing beats, - extracting one of (i) four primary sub-signals from the beat series and performing frequency domain analysis independently for each of the aforementioned at least four sub-signals, and (ii) four primary sub-signals and two derived sub-signals from the beat series and performing both time and frequency domain analysis independently for each of the aforementioned six sub-signals, wherein the four primary sub-signals comprise a first sub-signal indicative of pulse wave widths of the pulse wave; a second sub-signal indicative of an amplitude of the pulse wave; a third sub-signal indicative of an inter-beat time interval; and a fourth signal indicative of a degree of baseline variation in the pulse wave; and wherein the two derived sub-signals comprise a fifth sub-signal comprising the difference between the second sub-signal and the fourth sub-signal and a sixth sub-signal comprising sum of the first sub-signal and the third sub-signal; - combining, for at least three of the four primary sub-signals, the results of the frequency domain analysis for each sub-signal or the results of the time and frequency domain analysis for each of the six sub-signals, the combining comprising determining a group of estimates for the respiratory rate, the group of estimates comprising estimates of the respiratory rate determined using each of the sub-signals independently of the others; - calculating the final estimate for the respiratory rate by removing sub-signal estimates with poor signal-to-noise ratio and those that are statistical outliers. - gathering data related to a pulse wave in an electrical form, - extracting a beat series with noise removal and interpolated beats for missing beats, - extracting one of (i) four primary sub-signals from the beat series and performing frequency domain analysis independently for each of the aforementioned at least four sub-signals, and (ii) four primary sub-signals and two derived sub-signals from the beat series and performing both time and frequency domain analysis independently for each of the aforementioned six sub-signals, wherein the four primary sub-signals comprise a first sub-signal indicative of pulse wave widths of the pulse wave; a second sub-signal indicative of an amplitude of the pulse wave; a third sub-signal indicative of an inter-beat time interval; and a fourth signal indicative of a degree of baseline variation in the pulse wave; and wherein the two derived sub-signals comprise a fifth sub-signal comprising the difference between the second sub-signal and the fourth sub-signal and a sixth sub-signal comprising sum of the first sub-signal and the third sub-signal; (i) four primary sub-signals from the beat series and performing frequency domain analysis independently for each of the aforementioned at least four sub-signals, and (ii) four primary sub-signals and two derived sub-signals from the beat series and performing both time and frequency domain analysis independently for each of the aforementioned six sub-signals, wherein the four primary sub-signals comprise a first sub-signal indicative of pulse wave widths of the pulse wave; a second sub-signal indicative of an amplitude of the pulse wave; a third sub-signal indicative of an inter-beat time interval; and a fourth signal indicative of a degree of baseline variation in the pulse wave; and wherein the two derived sub-signals comprise a fifth sub-signal comprising the difference between the second sub-signal and the fourth sub-signal and a sixth sub-signal comprising sum of the first sub-signal and the third sub-signal; - combining, for at least three of the four primary sub-signals, the results of the frequency domain analysis for each sub-signal or the results of the time and frequency domain analysis for each of the six sub-signals, the combining comprising determining a group of estimates for the respiratory rate, the group of estimates comprising estimates of the respiratory rate determined using each of the sub-signals independently of the others; - calculating the final estimate for the respiratory rate by removing sub-signal estimates with poor signal-to-noise ratio and those that are statistical outliers.