Friday, June 29, 2012

Grocery Store Purchases

Last year, June was a good month for my personal weight loss. It is happening again this month. You will see that when I post the charts tomorrow. I was therefore curious which months we buy the most food.

Click to enlarge.

I started with the monthly grocery store sales as reported by the U.S. Census Bureau. I chose the data that was not seasonally adjusted since I am actually interested in seeing the seasonal patterns. That monthly data was divided by the number of days in the each month (including leap days where needed). The inflation as seen in the "Food at Home" data series from the BLS (also not seasonally adjusted) was used to put it in today's dollars. The total was divided by the reported population during that month.

I think the overall downward trend can be explained by the growth of wholesale food retailers like Costco and Sam's Club. That's certainly where I do the bulk of my food buying these days. There are other factors that are important too. I know people are eating out more in general than they once were.

Although I find this chart interesting, I actually made the chart to create the following one.

Click to enlarge.

This chart shows how much a given month is generally above or below the trend line in the first chart. As seen here, there are strong seasonal effects when it comes to food purchases. December is a big month and January we must be eating leftovers. That makes sense. May, June, and July are looking like the BBQ months. That makes sense too.

I'm having difficulty coming up with a theory to explain why October is so low. Maybe we feed ourselves on cheap Halloween candy before the kids even show up at our doorsteps? I can assure you with nearly 5% certainty that it has never been done in this household! ;)

And lastly, here's a chart showing December grocery store sales relative to the long-term declining exponential trend.

Click to enlarge.

As seen in the chart, December 2008 was actually 1.28% below the typical month's trend. Ouch. I have a very uneasy feeling that we'll be getting a repeat at some point. It could happen this year. It could take a few years. Who knows? We've passed the peak and the trend has never reversed once that's happened (since 1992 anyway). Maybe this will be a first, but I'm not exactly bracing for the perfect pudding. Let's just put it that way.

Source Data:
U.S. Census Bureau: Retail Trade
St. Louis Fed: Population


Mr Slippery said...

Very interesting monthly trends. Instead of BBQ for May, June, July, I suggest that it is because the kids are home for the summer with school out.

September and October could be school effect in reverse. Kids eating more at school and less at home. Just a guess.

Scott said...

Interesting analysis. I prefer to look at NSA data as well. My theory on October is that there is nothing on the calendar that stores can use as a promotional gambit.

Walmart moving into groceries in a big way has probably had a big effect on the $ per capita as well. The stuff they stock is going to be at lower price points relative to grocers.

I think to some degree brand name processed foods are pricing themselves out. The shrinkage of package size has been very noticeable, with potato chips, for example. Where I would buy this product occasionally, I now just walk past that aisle. Whatever taste temptation is destroyed by the price.

Stagflationary Mark said...

Mr Slippery,

Your theory seems pretty good.

I thought up another possible reason last night. Mother's Day, Father's Day, and 4th of July? Just a thought.

Stagflationary Mark said...


The shrinkage of package size has been very noticeable, with potato chips, for example.


n 2002, Nestlé insisted on a smaller container to increase profits and so the standard US half gallon (2 quarts) container (1.89 L) was down sized to 1.75 quarts (1.65 L) container. In May 2008, the 1.75 quart container was further downsized to 1.5 quarts (1.42 L). Other ice cream manufacturers followed the downsizing move.

Very annoying. I like to buy in bulk to save money. I resent the trickery here and therefore tend to buy less of it overall (out of spite).

My girlfriend's is this.

Banquet Fried Chicken Meal

New Large, Meaty Thigh!

Yeah, too replace the two pieces of chicken you once got. The total calories went down. Less food, same price. Woohoo.

Stagflationary Mark said...

Ack. Too replace? Behold the power of Benadryl (for allergies) to keep my mind sharp, lol. Sigh.