A method of determining whether a culture in a vessel contains a plurality of microorganisms, the method comprising: calculating a normalization relative value for each respective measurement in a plurality of measurements of a biological state of the culture in the vessel, taken at different time points between a first time point and a second time point, between (i) the respective measurement and (ii) an initial biological state of the culture taken at an initial time point, thereby forming a plurality of normalization relative values; determining, for each respective predetermined fixed interval of time points between the first time point and the second time point, a first derivative of the normalization relative values for measurements of the biological state in the respective predetermined fixed interval of time points, thereby forming a plurality of rate transformation values, wherein the plurality of rate transformation values comprises a plurality of sets of rate transformation values, wherein each respective set of rate transformation values in the plurality of sets of rate transformation values is for a different set of contiguous time points between the first time point and the second time point; computing, for each respective set of rate transformation values in the plurality of sets of rate transformation values, an average relative transformation value as a measure of central tendency of each of the rate transformation values in the respective set of rate transformation values, thereby computing a plurality of average relative transformation values; obtaining (i) a first result based on a determination of whether any average relative transformation value in the plurality of average relative transformation values exceeds a first threshold value or (ii) a second result based on a determination of whether an extent of growth exhibited by the culture exceeds a second threshold value; and using the first result or the second result to determine whether the culture in the vessel contains the plurality of microorganisms. calculating a normalization relative value for each respective measurement in a plurality of measurements of a biological state of the culture in the vessel, taken at different time points between a first time point and a second time point, between (i) the respective measurement and (ii) an initial biological state of the culture taken at an initial time point, thereby forming a plurality of normalization relative values; determining, for each respective predetermined fixed interval of time points between the first time point and the second time point, a first derivative of the normalization relative values for measurements of the biological state in the respective predetermined fixed interval of time points, thereby forming a plurality of rate transformation values, wherein the plurality of rate transformation values comprises a plurality of sets of rate transformation values, wherein each respective set of rate transformation values in the plurality of sets of rate transformation values is for a different set of contiguous time points between the first time point and the second time point; computing, for each respective set of rate transformation values in the plurality of sets of rate transformation values, an average relative transformation value as a measure of central tendency of each of the rate transformation values in the respective set of rate transformation values, thereby computing a plurality of average relative transformation values; obtaining (i) a first result based on a determination of whether any average relative transformation value in the plurality of average relative transformation values exceeds a first threshold value or (ii) a second result based on a determination of whether an extent of growth exhibited by the culture exceeds a second threshold value; and using the first result or the second result to determine whether the culture in the vessel contains the plurality of microorganisms.