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Does the BPM of music playing in a grocery store change the way people shop?

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We went to 20 different grocery stores on 3 weekends to run our study.  Our experimental units were the shoppers, but we did not know them individually, just as a collective whole.

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The 20 grocery stores were picked randomly, but the store managers had to agree to let us run the experiment.  We selected 10 Fry's, 5 Safeway, 2 Albertson's, and 3 Sprouts stores.

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We played lyric free music with a BPM of 90+ in the grocery store one weekend (Saturday 7am until Sunday 7pm).  The next weekend we returned and played music with a BPM of 70 to 80. The third weekend we had NO music playing in the background while people shopped.

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Our explanatory variable is whether the shoppers listened to fast or slow music while they shopped, as defined by the BPM of the music.

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We will measure the total sales of the grocery store we are running the study at each weekend, to see if the BPM of the music has had an effect.

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We randomized the stores we picked to make sure the locations are diverse across the Phoenix-Metro area. We still have lurking variables like what type of music the shoppers are used to, and any special events/holidays surrounded the weekend we were testing on, which might have impacted sales.

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Every grocery store will act as its own control group, since the third weekend of the study will consist of no music playing. We will be able to compare sales data across all three weekends this way.

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Our shoppers will be blind in this study, meaning they don't know which treatment they are receiving. In fact, they don't actually know that they are part of the study. We do not have a double-blind, because the researchers on our team know what type of music they are feeding into the store.

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We are using crossover design for this study, as each store will go through all three treatments on three different weekends. This allows us to have better data, so that we can be sure that sales changes were actually due to the music playing.

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We are running this study with 20 stores, so our margin of error is 22.36%.  This is a large margin of error, which is not necessarily good, but sampling more stores would be time consuming and expensive.  In reality, our study is measuring results from thousands of shoppers, we just don't have them identified as subjects in our study, since we don't know who they are.

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This study could be replicated in the future, with an additional study where even more stores are studied. We may consider adding more treatments or looking only at a single store for an entire year of sales. Replication adds confidence in results. With such a small number of stores being tested, replication is probably needed to validate our results.

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The fast music lead to a decrease in sales of around $21,000 on average. The slow BPM music lead to an increase in sales around $2,000 per store on average.

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The increase in sales with slow BPM was small, but 19/20 stores did have an increase in sales with slow BPM music. Almost every store had a decrease in sales when the BPM was fast. Based on these results, we have determined the difference to be statistically significant.

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We have a team of 20 researchers, who were paid hourly ($15 per hour)  on those three weekends.  They worked a total of 60 hours on this research project.  Each store volunteered/agreed to be part of this study, so there was no cost there.  We did give each store manager a $100 gift card to thank them for their time and courtesy.
Salaries: 20 x 15 x 60 = $18,000
Gift Cards: 20 x 100 = $2000
TOTAL COST: $20,000

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Our study was replicated by our team with more stores and various levels of BPM. Results were confirmed and it was found that stores playing music with a BPM of 70 or less had a 15% increase in sales overall. The results were published. As a result 2 major grocery chains (Kroger and Sprouts), changed the music they play in their stores. Keeping slow music playing causes shoppers to slow down, spend their time shopping, and therefore buy more products.