# Things I have learned about trackables--Time-based Survivorship

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The earlier posts discussing survivorship were event- or drop-based.  That is, what percent of trackables remain after each drop.  However, that only tangentially addresses questions centering on how long travel bugs last. For this post, survivorship was determined for each of consecutive six-month periods, out to nine years.

I used the same spreadsheet as in earlier calculations, an unsorted portion of which is shown below.  The data consists of the first 1,710 trackables released in the calendar years 2010-14.  The activity of every trackable was followed through the end of 2019. The E1 and all the C columns are calculations of the total days a drop occurred after the travel bug release...these are the fodder for this post.

Now consult the table below. The Yrs column is the six-month intervals under study.  The Days column is the six-month interval converted to days. These values were used to determine the number of last-logs occurring on or before that number of days. The n column is the number of last-logs returned by each series of sorts. The Percent Remaining column is the respective n converted to a percent. The Percent Loss column is the percent decline from the previous six-month period.

One thing to bear in mind when interpreting these results is that, while the average number of drops per six-month period is between two and three, travel bugs do not move on a regular schedule.  Thus, for any given trackable, in any given period, the actual number of drops per six months is observed to be as few as none to as many as five drops.

The graph (see below) is the percent remaining plotted against each six-month interval. The overall shape of the time-based curve is not materially different than the drop-based curve.  Both show half of the losses occur in the year to year and a half period, or within the first five to six drops.

Again, trackable survivorship is much higher in Europe than in the United States.  Trackables represented by the left side of the curve were almost exclusively (95%) released in the US and is marked by a precipitous decline.  The more-attenuated right side of the curve represents trackables mostly in Europe .

Should anyone doubt the European influence on the curve, I have appended the ID numbers of the 35 trackables that survived longer than seven years. Those in red text (11 total) were never dropped outside North America. Although they all lasted for the requisite seven years, many of them have very few drops interspersed with long periods of inactivity.  That is a thought I will expand upon in a later post.  Those trackables in green text (2) were released in Europe and were never dropped in North America.  Those in blue text (22) were released in the US, but at some point found their way off this continent, mostly to Europe.

Finally, this is a report on the activity of my travel bugs.  I believe, in the main, these data will represent any other US-based collection.  However, more access to traveling cachers and regional differences in stewardship can modify the curve to some extent.

TB4085Y, TB3M3W7, TB40CX1, TB3ZX3T, TB3ZX48, TB40C6C, TB3EAJ1, TB403K1, TB2T1KW, TB33NPQ, TB33NRJ, TB2REAY, TB2REBJ, TB2REA1, B2T1MC,  TB48HJD, TB2T1NF, TB48Q2E, TB48HJV, TB48HKK, TB493Z1, TB40CVX, TB40CX0, TB33QQE, TB48Q1X, TB3ZX3V, TB3MRHQ, TB3EAHP, TB40CWB, TB3ZX38, TB3MRJT, TB4086W, TB3M3WV, TB2T1KN, TB3EAJH.

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The curve seems quite exponential... Amazing how only 72% survive the first 6 months. Thanks for the helpful graph ??? Another graph idea: How likely is it for a TB to come back into play after n months of inactivity.

You might get an idea from my earlier post on drop intervals.  There is some chance they will reappear after a year, but, although it does happen, anything that is inactive for two or more years has a small chance of getting back into circulation.  This is based on how my travel bugs were treated.  It may be different for another collection, but I doubt it will vary much.

You might get an idea from my earlier post on drop intervals.

Thanks, interesting stuff!

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