The Statistics of Forever

Effect of Probability on Preservation-1

I recently presented a talk titled “Preservation Is Forever.” In this talk, I reviewed the Terms of Service for many online services offering photo products and digital storage. Many of these services have terms indicating that they can delete photos after a period of time (typically one year without ordering) or otherwise discontinue or change their service. These statements are correct, but they should not be interpreted as indicating that they will do this, only that their is a risk of something bad happening.

Here’s where we need to discuss statistics. If there is a 10% chance of something bad happening in a given year, after seven years your photos are more likely to be lost than preserved.  With a 20% chance of of loss, this time decreases to four years. The same problem happens if we assume lower probabilities, although it takes longer. With a 5% chance of loss, your data is more likely to be lost than preserved after 14 years, and with a 2% chance of loss your data is likely lost after 35 years.

What is the actual chance of loss? I don’t know, but my estimate is that in any given year, the probability for loss is between 5 and 10%, given the many things that can change with online businesses. If this is in fact the case, then Forever, which states that it will preserve your data for your lifetime plus 100 years, is really the only option for long-term preservation. The reason Forever meets this need is because the Forever Guarantee Fund provides the resources to ensure long-term preservation, eliminating risks associated with other online businesses.

Note: To calculate years lifetime, use the formula Y=Log(0.5)/Log(1-p), where Y represents the expected lifetime in years, 0.5 represents 50% chance of data preservation, and p is the annual probability of data loss.


About Mark Mizen

I have over twenty years professional experience in all aspects of photography and digital imaging. I am Chair of the ISO WG5 TG2 committee responsible for physical properties and durability of imaging material and am currently with HID Global working on systems for security printing for IDs, licenses, and credit cards. Previously, I was Director of Digital Development at Creative Memories from 2009 to 2012 and was responsible for the Creative Memories digital products and services. I also established and directed the Creative Memories Technology Center, which evaluated new products prior to product introduction, assisted with production difficulties, and provided technical information to support product sales.
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3 Responses to The Statistics of Forever

  1. Dr. Mark – but how can they guarantee “forever”? What if they go out of business as other companies have done?

    • Mark Mizen says:

      The Forever Terms of Service are for your lifetime plus 100 years. They accomplish this by putting a large portion of the initial fee into an endowment to fund future operation. Annual expenses for storage require a 4% withdrawal rate, which investment income is sufficient to fund.

  2. Pingback: Forever Live! Video Now Available | All About Images Blog

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