Vísitalan

Vísitalan is a statistical concept used to express the relative change in a variable over time. In its standard form, a vísitala (index number) compares the value of a measurement in a given period to that in a base period, and is typically scaled so the base period has a value of 100 (or 1). The resulting figure shows how much the quantity has increased or decreased since the base period.

Calculation can be simple or weighted. A simple index uses the ratio of current value to base value multiplied by the base index. A weighted index assigns different importance to components, as in price indices where expenditure shares are used. Common methods include Laspeyres, Paasche and Fisher indexes, and chain-linked indexes which update weights over time.

Vísitalan has broad applications. It is used to track inflation through price indices such as the consumer price index, to measure real growth in GDP, to compare living costs across periods, and to construct financial and economic indicators for policy and research.

In Iceland, as in many countries, statistical agencies publish vísitölur. The term vísitala is widely used for index numbers, for example vísitala neysluverðs (consumer price index) and other sectoral indices produced by Hagstofa Íslands. These figures help monitor price movements, cost of living, and economic performance.

Historically, index numbers were developed in the 19th and early 20th centuries to provide a compact summary of relative change. Today they remain a fundamental tool in statistics, economics, and finance for comparing values across time and space.