DETECTION OF OUTLIERS IN THE CANADIAN CONSUMER PRICE INDEX (CPI) ABDELNASSER SAÏDI AND SUSANA RUBIN BLEUER STATISTICS

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# DETECTION OF OUTLIERS IN THE CANADIAN CONSUMER PRICE INDEX (CPI) ABDELNASSER SAÏDI AND SUSANA RUBIN BLEUER STATISTICS - PowerPoint PPT Presentation

DETECTION OF OUTLIERS IN THE CANADIAN CONSUMER PRICE INDEX (CPI) ABDELNASSER SAÏDI AND SUSANA RUBIN BLEUER STATISTICS CANADA. What is the CPI ?. Is a weighted arithmetic average of price indexes over all basic classes. The weights are obtained from the survey of households spending.

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## DETECTION OF OUTLIERS IN THE CANADIAN CONSUMER PRICE INDEX (CPI) ABDELNASSER SAÏDI AND SUSANA RUBIN BLEUER STATISTICS

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ABDELNASSER SAÏDI AND SUSANA RUBIN BLEUER

What is the CPI ?
• Is a weighted arithmetic average of price indexes over all basic classes. The weights are obtained from the survey of households spending.
• the price index at the basic class is in turn a weighted sum of the micro indexes over all the items in the class.
• The micro index is a geometric mean of the price relatives of n outlets surveyed.
CURRENT EVALUATION PROCEDURES
• Large amount of resources used to correct a small number of errors.
• verifications made manually:
• Verification of all records with status ‘special’.
• Verification of all records with a relative price increased or decreased by 15%.
• Editing procedures related to missing values, missing outlets and quality changes (see Allard-Saulnier and Beyrouti (2003)).
PROPOSED EVALUATION PROCEDURES
• Performed on an editing group
• All observations pertaining to a particular item
• and in a particular geographical area ( 4 possible levels)
• and having the same status code if the percentage of “SP’s” > 15%.
• status code “ SP’s ”

( regular → special or special→ regular).

PROPOSED EVALUATION PROCEDURES
• Methods considered :
• ILO Tukey and variants,
• MAD (Median Absolute Deviation),
• Quartile method and HB (Hidiroglou-Berthelot)
• RFM (Resistant Fence Method)
• Detection method with higher breakdown point than Tukey’s method and taking into account the skewness of the distribution and the small size of the CPI sample are favoured
• Quartile method with asymmetric fences applied to the log of the price relatives was recommended
INFLUENCE IN THE BASIC CLASS
• Contribution of each outlier on the basic class index
• Analysis of the percentage of contribution
• How to define a cut-off to identify influent observations ?