Inflation is a much-talked-about economic indicator that measures the rate of increase in the prices of goods and services over time. But how exactly is inflation measured? There are a few key methodologies economists use to track price changes and quantify inflation.
The Consumer Price Index
The most common measure of inflation is the Consumer Price Index (CPI). The CPI tracks the prices paid by urban consumers for a basket of goods and services, including food, housing, apparel, transportation, medical care, recreation, and education.
The CPI basket includes over 200 categories of items that represent typical consumer spending. The relative importance of each item is weighted based on expenditure data gathered through consumer surveys. The weightings are updated periodically to account for changes in spending habits.
Every month, data collectors visit or call thousands of retail stores, service establishments, rental units, and doctors’ offices all over the country to obtain price data on the specific items in the CPI basket. The prices are averaged together with appropriate weightings to calculate the CPI.
The CPI is reported as a percent change from a baseline reference period. The reference period used is 1982-1984, which equals an index value of 100. For example, if the CPI for June 2022 is 300, that means the average prices consumers paid for goods and services in June 2022 were triple the average prices paid for the same mix of goods and services during 1982-1984.
The most commonly reported CPI figures are based on all urban consumers (CPI-U) and urban wage earners (CPI-W). The CPI-U covers approximately 93 percent of the U.S. population, while the CPI-W is a subset relating to households where more than one-half of income comes from clerical, wage supervisor, and manual labor occupations.
The GDP Deflator
Another important gauge of inflation is the GDP price deflator, which measures price changes for all goods and services produced in an economy. While the CPI tracks prices paid by consumers, the GDP deflator tracks prices received by producers.
The GDP deflator is calculated by dividing the current dollar GDP by real GDP. Current dollar GDP measures production at current prices for a given year. Real GDP adjusts current dollar GDP for inflation to give a sense of underlying production volume.
For example, say the current dollar GDP increased from $1 trillion to $1.03 trillion over one year. Over the same time frame, real GDP held steady at $1 trillion. The $30 billion increase in current dollar GDP over and above the $1 trillion base reflected price increases rather than more actual goods and services being produced. As such, the GDP deflator would be calculated as $1.03 trillion divided by $1 trillion, or 1.03 – indicating an average price increase of 3%.
Since the GDP deflator is not based on a fixed basket of goods, it captures price changes across the entire economy. This provides some advantages over the CPI in assessing inflationary impacts. However, the GDP deflator is only available quarterly and with a lag of several months, unlike the monthly CPI.
The Producer Price Index
The Producer Price Index (PPI) is another important metric that tracks inflation before it reaches the consumer level. The PPI measures average price changes received by domestic producers for their output. This includes goods sold in wholesale markets and services provided by other businesses, government, and nonprofits.
There are thousands of individual PPI commodity and service indexes that are aggregated into major industry groups and general indexes. The weights are derived from Census survey data on the value of receipts for each item.
The PPI is a valuable leading indicator of CPI inflation, signaling cost pressures that will eventually face consumers down the production chain. It also provides insights into industry-specific inflation dynamics. Two commonly cited PPI measures are the index for final demand and final demand excluding food and energy, which strips out volatile categories.
The Personal Consumption Expenditures Price Index
The personal consumption expenditures (PCE) price index is a measure of inflation compiled by the Bureau of Economic Analysis along with the PCE spending data that feed into GDP calculations. The methodology is similar to CPI in tracking prices paid by consumers, but PCE covers a broader basket of goods and services and uses different weighting constructs.
PCE also tends to revise its methodologies more frequently than CPI to account for shifts in consumer behavior. For example, PCE updated its housing inflation measures much earlier than CPI to account for rising rents and homeowners’ equivalent rent.
The Federal Reserve officially targets the PCE price index rather than CPI for its 2% average inflation objective. This is because PCE is believed to better reflect the whole economy’s inflationary trends. Headline PCE and core PCE excluding food and energy are closely monitored.
Weighting Methodologies and Shortcomings
While the consumer price and producer price indexes outlined above seem straightforward in concept, there are complex technical challenges in how they are constructed. Changing consumer behaviors, the emergence of new products, adjustments in quality, and shifts in the relative importance of items over time can bias inflation metrics.
Statisticians make continuous efforts to update weighting methodologies and modify samples. But no inflation measure perfectly captures the nuanced multitude of prices faced by millions of diverse households and businesses across the entire economy.
Still, the core CPI and PCE benchmark indexes have proven fairly reliable over time in tracking broad inflation trends, despite their limitations. They provide standardized metrics that allow meaningful historical comparisons in prices and purchasing power over many decades.
Inflation measurement involves tracking changes in the prices of thousands of individual goods and services using weighted indexes. While the Consumer Price Index is the most familiar indicator, metrics like the GDP deflator, Producer Price Index, and Personal Consumption Expenditures Index provide complementary perspectives on national and industry-specific inflation. There are ongoing efforts to refine methodologies, but inherent limitations mean inflation gauges must be interpreted with care. The core indexes do however give reasonably accurate high-level views of inflation over time.
Frequently Asked Questions
What are some common causes of inflation?
Some common drivers of inflation include expansionary monetary policy, rising wages, supply chain disruptions, profit margin increases, currency devaluation, demand-pull pressures, and cost-push shocks like energy price spikes. Inflation is ultimately a monetary phenomenon but can have multiple contributing factors.
How does inflation impact consumers?
Inflation erodes consumer purchasing power over time as more money is needed to buy the same goods and services. It also reduces the real value of savings and fixed incomes. Unanticipated high inflation can be very detrimental to consumers’ financial planning and standard of living.
How does inflation impact the broader economy?
High sustained inflation can lead to misallocation of resources, loss of competitiveness, distorted price signals, arbitrary wealth redistributions, and uncertainty – all of which dampen productive economic activity. However, low stable inflation is generally beneficial, encouraging investment and risk-taking.
Why do economists track core inflation rates?
Core inflation indexes that exclude volatile categories like food and energy provide a better sense of underlying long-term inflation trends that are more responsive to monetary policy. Headline measures can be heavily skewed by temporary supply shocks.
What are the costs involved in collecting inflation data?
The Bureau of Labor Statistics has an annual budget of around $640 million to compile the various Consumer and Producer Price Indexes. This covers expenses for data collectors, commodity analysts, statistical modeling, quality adjustments, and publication. Reliable high-frequency inflation data is expensive but essential.