What determines price fluctuation of groceries
"Yes and no. First off, commodity prices reflect the cost of a good about 3 steps back in the retail supply chain; the agreed-upon price for the raw foodstuff between farmers/ranchers and manufacturers. Your grocer may carry bags of whole grain wheat, but that's certainly not all he carries that contains it. Same for corn, rice and other staple grains, as well as for fruits and vegetables, herbs (yes, you can buy basil by the ton on the CME), meats, various sugars, etc. So, a long-term sustained change in prices of a commodity foodstuff will eventually affect the real cost to you to buy things they're made from. However, in the short term, the retail supply chain will generally act as a buffer between these prices and the ones you see on the store shelf. Consumers don't like price increases, especially of necessities like food. When food costs go up, consumers can and will very quickly change their spending habits, buying cheaper options to get their needed calories. That makes manufacturers nervous; consumers not buying their product is a worse scenario than consumers buying their product at a reduced gain or even at a loss. So, manufacturers, and suppliers and retailers, will all absorb as much as they can of the cost of a commodities increase before beginning to pass it on to consumers. On the flip side, while consumers like price drops, they don't notice them as much as price increases. So, the supply chain will also absorb a fall in commodity prices by resisting price reductions in the consumer goods, as long as they can get away with it (which is usually longer than the price reduction actually lasts). The net effect is that processed food prices typically follow the gentle upward climb of long-term inflation, and only rarely do you see drastic price increases or decreases. Where this model breaks down a little bit is in highly perishable foodstuffs, especially seasonal or ""wild-managed"" foods; fruits and vegetables, seafood, etc. The limited time in which the stuff can be sold makes the process of getting a fish out of the ocean and a fruit off the tree and into your grocery store much more market-driven; the producers, suppliers and grocers are all in constant contact over what's available and how much they can get for what price. The prices therefore are typically a lower markup (unlike highly processed grain-based foods, there's not much added value to be marked up between the apple farmer picking the fruit and the grocer putting it on display), but also much more volatile; if there's a bumper crop of fruit, the farmer has to unload it all or it goes to waste, while similarly if an early freeze decimated the apple crop, the suppliers can't just get some of last year's bumper crop out of storage; they fight with everyone else for what little made it to market. Farmers will sometimes intentionally let excess crop spoil in order to maintain a minimum price for what they sell (the rest can at least be composted and used for fertilizer, saving them some money on maintenance), but there's no silver bullet for a shortage. This is why a lot of these foods, especially seafood, are considered luxury items; they're not stable enough for everyone to get as much as they want whenever they want, unlike staple grains." "No. Some grocery stores may discount specific products based on inventory to drive sales using ""loss leaders"" where the product is intentionally priced as a loss for the business. While commodity futures may impact some prices, I'm not sure one can easily extract the changes solely due to futures shifts." That is true. Since commodities are basically a futures contract, their actual price is not reflected in grocery stores. It is more of a supply and demand issue with your grocer.
It is very likely that the fund paid out a dividend in the form of reinvested shares.  This happens with many funds, especially as we come to the end of the year. Here's a simplified example of how it works.  Assume you invested $1000 and bought 100 units at $10/unit.  Ignoring the daily price fluctuations, if the fund paid out a 20% dividend, you would get $200 and the unit price would drop to $8/unit.  Assuming you chose to reinvest your dividends, you would automatically purchase another $200 worth of units at the new price (so 25 more units).  You would now have 125 units @ $8/unit = $1000 invested. In your example, notice that you now have more shares than you originally purchased, but that the price dropped significantly.  Your market value is above what you originally invested, so there was probably also a bit of a price increase for the day.  You should see the dividend transaction listed somewhere in your account. Just to confirm, I did a quick search on ICENX and found that they did indeed pay a dividend yesterday. My household items/groceries comes from too many different places, from Costco, Amazon, Sprouts, local grocers, and farmers markets. Never bought groceries on Amazon though, no perishables or too expensive for packaged goods.     I sure wont pay WFM prices for their 360 store brand I think it has more to do with Amazon Go than grocery delivery. Companies have been trying to make online grocery delivery services popular for decades now.  However, it still only represents about 1-2% of the grocery sales.  I am sure Amazon will do what they can to make delivery more popular, but Amazon Go and the Whole food purchase looks like Amazon has figured-out most people prefer to go to the grocery store. You're spot on for Whole Foods. This is a great step for them, and for Amazon. I've spoken with coworkers across my company that have been severely disappointed in the past with the Amazon grocery development. I see this as a easy way for Amazon to enter brick-and-mortar, compete in a more tangible way with other grocery chains, and still be Amazon.   Ultimately, Whole Foods/Amazon does not equivocally mean better prices from farm marketers. Grain, pork, corn, beef, salt prices are going to if anything lower for farmers for larger profits as the marketers have not changed. Monsanto, ADM, Cargill, are still big players that are all in talks with to make this merger sustainable for Amazon and Whole Foods. That supply chain remains until Amazon moves into a rather deeper market. I asked how often grocery purchases are made in a comment, but I'm going to assume weekly for simplicity. If a roommate is present during the week following a grocery purchase, then they owe a share according to their preferences as you outlined them above. You will have to track the grocery cost by category for that week and calculate the balance owed by the person for that week. If there is a partial week where most expect to leave for a holiday or otherwise, then fewer groceries should be purchased for that week, and the cost of shares will decrease accordingly. One need only indicate preferences once, and weekly attendance thereafter. The only issue remaining is to determine how to record shares. If a normal person consumes 3 shares of milk, and .5 shares of butter, and so on, you simply add up all of the milk shares for the week and divide the milk bill by those shares. Same with the butter. The downside of this method is that you have to predict consumption in advance, so you may instead calculate by consumption after the fact with a deposit paid by all to create the initial grocery supply which will be refunded when that person leaves the grocery purchase co-op, and shares are calculated by who participated in the week prior to the grocery purchase. This also allows for a mid-week refresh if any commodity incurs higher than expected consumption, with the mid-week bill being added to the end of week refresh trip. Excellent explanation. Upvote to you sir. I would like to add something:  How do we know how many bushels of apples is worth a chunk of deer meat?   You did not touch on the concept of value.  The way I see it, value is related to the human energy required to procure a specific good.   For example: it takes a man all day to find a nugget of gold, while it take another man all day to pick 20 bushels of apples. Because gold is scarce, it is worth a lot of apples: it has a high value.   At it's core, value is assigned based on the amount of human labor required to acquire a good or service.   For example: Many years ago there may have been an equal number of bears and skunks. However, it would take many brave hunters with bows and arrows to kill a bear, while any hunter could kill a skunk solo. Thus, even though they had the same scarcity, a bear hide would be more valuable because the human labor required was greater.   Many economics classes simply say value depends on supply and demand. However, if something is in low supply and high demand, it is BECAUSE it takes so much human effort to procure. If it did not take large amounts of human labor, everyone would sell said item and the value would drop.   What is your take on this? do you have a better explanation for value? For the CPI, there is actually federal employees whose job it is to visit various stores to collect the prices of specific items (boy's size-14 collared shirt made of 97 percent cotton).  Planet Money did a great podcast on this, actually following one of these people for a day. In a free market, supply and demand control the equilibrium point of a commodity. Price is one of the variables that moderates demand.  But the problem is - 'employment' isn't a free market - you cannot freely decide not to accept a job, because you need _some_ income to live.   The wage of an employee - especially at the 'unskilled' tier - is much more about availability of workers vs. jobs. And better yet, those jobs can be subdivided into shifts, and so you can employ _more people_ for _less hours_ or vice versa.   The employer therefore has a lot of control over effective wages as a result, and it's only tenuously connected to the 'free market' of the value of service of a burger.   So I'd guess the 'market value' would steadily drop to 'about the cost of living in the local area' - maybe a little below even, because you can still employ people who are partially subsidised by family. And further still, you can have people subsidising _themselves_ by working additional hours.   So I reckon you'd get equilibrium at 'about' 90% of local cost of living, if you work an 80 hour week.