- Definition: PPI measures the development of prices of sold production of the industry (mining and quarrying, manufacturing, electricity, gas, steam and air conditioning supply and water supply; sewerage, waste management and remediation activities). The price index reflects price changes as well as changes in the structure of sales and structure of assortment due to calculating prices as quotients of values and quantities of their monthly sales including all transactions and all sales directions (domestic and export).
- International standards: The definition of PPI is in accordance with Eurostat recommendations and Short-term Statistics Manual.
- Classification: Polish Classification of Activities based on NACE Rev.2;
- Polish Classification of Goods and Services based on NACE Rev. 1.1, CPA and PRODCOM.
Scope of the data
- Industrial coverage: Mining and quarrying, manufacturing, electricity, gas, steam and air conditioning supply and water supply; sewerage, waste management and remediation activities. All industries are included in the index.
- Product coverage: The survey covers products selected by enterprises from those sold in a given month including all sales directions. There are about 19,000 individual price observations per month. Products within both primary and secondary activities of enterprises could be included in the survey.
- Geographic coverage: Entire area of the country.
Types of prices: The survey includes net transaction prices received by producers for products sold within the reference month. The prices exclude the value-added tax and are available both with excise tax (so-called the "producer prices") and without excise tax but with subsidies (so-called the "basic prices"). "Producer prices" were used to compile indices for 1993-1995 period, from 1996 onwards - "basic prices" are used.
Source data collection programs
- Establishment selection: Purposive. The selection and updating is made by the CSO in co-operation with regional statistical offices on the basis of the National Economy Units Register (REGON) and the Statistical Units Database (BJS). The main criteria are annual values of sold production of enterprises and their share of production in the respective NACE class.
- Product/transaction selection: Purposive selection of product groups and products themselves is made by reporting enterprises in co-operation with regional statistical offices. The criteria are defined by CSO, in which volume and value of sales are the most important.
- Product/transaction specification: Every product has detailed, tighted specification given in the form by reporting enterprise. For a proper identification, the specification generally includes a detailed name, brand, technical parameters, material used if necessary, and a measurement unit.
- Sample sizes: About 3,300 units, i.e. 10 percent (in 2009) of the total number of enterprises with 10 and more employees. The total sales value of these 3,300 units exceeds 60 percent of the total sold production of enterprises with 10 and more employees.
- Price collection methods: Electronic questionnaire filled in on CSO’s Internet website. Some prices (i.e. centrally determined) are collected by the CSO in form of price lists.
Source data timeliness
- Timing of price observations: Prices of all products are collected every month. There is no set date in the month for data collection. A price is a quotient of value and quantity of whole monthly sales of the product.
- Period of current index weights: Annual sold production value from 2005. For current weighting - monthly sold production value in the current month.
- Frequency of weight updates: Generally weights are updated every five years; in the period of 1992-1996 - more frequently due to significant methodological and classification changes.
Source data statistical techniques
- Sources of weights: Weights are derived from annual sold production net-data obtained from the industrial survey, which covers in sections B, C, D and E of NACE Rev.2 all enterprises with 50 and more employees and sample (10 percent) of enterprises with 10-49 employees. For the current weighting (while computing price indices in the current month to the previous one) monthly sold production net-data obtained from both the price survey and the industrial survey are used.
- Computation of lowest level indices: The lowest level indices are price relatives of the average price of individual representative product of the current month to the average price of this product for the previous month multiplied by 100.
- Aggregation formula: At the first stage, individual product indices are combined using Paasche formula and current weights (monthly sales values) to obtain monthly price indices (previous month =100) for enterprises and next for all digit levels of NACE. At the second stage (after weights' price updating) Laspeyres type chain index is used for obtaining the other price indices, e.g. corresponding period of previous year = 100; 2005 = 100.
- Aggregation structure: Product price indices are aggregated to the level of enterprises, next are calculated indices for 112 groups, 34 divisions, 4 sections of NACE and the industry as a total.
- Alignment of value weights and base period: At the first stage of aggregation, the weights refer to the current month and prices - to the current and the previous month (Paasche). At the second stage, weights refer to 2005. To align value weights and base period - the price updating approach is applied
- Linking of reweighted index to historical index: Historical series are constructed using a chain method.
- Reference period: 2005, previous month = 100 and others.
Other statistical procedures
- Treatment of missing prices: When a price observation is unavailable in a given month, this price is not imputed and this item is removed from index calculation. Its replacement is selected during next month survey, based on the above mentioned criteria of the selection. When a previous price observation reappears after one or more months then the enterprise estimates this price for the previous month.
- Selection of replacement items: Reporting unit selects replacement item analyzing structure of sales value, based on the above mentioned criteria of selection.
- Adjustments for quality differences: The survey does not include any adjustments for quality differences. Products with quality change are treated as totally new ones.
- Introducing new products: A list of products is updated by enterprises every month using current sales data. New products are introduced by reporting units when they gain significant shares in sales structure and fulfil the criteria of selection
- Seasonal items: When seasonal item is temporarily not available, it is removed from the calculation. It enters the sample again while appearing on the market with a significant share.