sentences:  A Divisia index is a theoretical construct, a continuous-time weighted sum of the growth rates of the various components, where the weights are the component's shares in total value.For a Törnqvist index, the growth rates are defined to be the difference in natural logarithms of successive observations of the components (i.e.their log-change) and the weights are equal to the mean of the factor shares of the components in the corresponding pair of periods (usually years).