What explains retail price variance over time

The covariates are NB (national brand vs. private label), PROM_FRQ (price promotional frequency), PROM_DPT (price promotional depth), CAT_CONC (category concentration), NRBR (number of brands in the category), STOCK (ability to stockpile) and IMPULSE (is the product an impulse good). Measurement details are provided in Appendix B. ................
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