Chart Consistency Index (CCI) Tool

I've put together a tool that will calculate how similar two weeks' charts are based on the later week's top 25 artists.

The tool will generate a Chart Consistency Index (CCI), which is a number ranging from 0 to 100. 100 means that the top 25 artists are the same both weeks, and in the same order. 0 means that none of the artists in the top 25 in the later week were in the earlier week's chart.

A CCI greater than 70 means that the two charts are substantially similar--most of the differences will be due to the artists being in a different order. A CCI less than 30 means that the charts are substantially different, with many of the artists having not been in the earlier week's chart at all.

Check it out at http://quinnsoft.com/random/lastfm_consistency.php. Please post any feedback you might have, positive or negative, including suggestions to improve the tool.

UPDATE: Added monthly CCI and average weekly CCI. Note that the "monthly" CCI actually compares 4-week periods, not months.

I have updated the tool with the option for a monthly CCI and average weekly CCI (up to 10 weeks).

The monthly CCI will combine four weeks of charts to compare with another four weeks of charts.

The average weekly CCI will simply average the CCI for a number of weeks compared to the previous week.

I have tweaked the algorithm a bit so that the higher ranked artists are appropriately given greater weight. There was a bug that caused the higher ranked artists to get only marginally higher weights in some profiles.

With the new algorithm, charts with very few artists will see the higher ranked artists weighted significantly higher than in charts with many artists.

Fixed. My input sanitizer was a bit overzealous--it was allowing only numbers and letters.

UPDATE (June 8): I have just fixed a bug with the monthly charts that occurs when there is an artist in your charts with 0 plays. I have also added profile/signature images with your CCI. For now, you have to go back to my site to update the jpg but I'm hoping to make it automatic in the near future.

You may have noticed that the CCI calculator was not working between January 29 and February 25. This is because Last.fm broke the 1.0 API.

The 1.0 API is working again; thus, the CCI calculator is back in operation. I hope to switch to the 2.0 API when I have the time to avoid this from happening in the future.

Due to this problem, I have deleted all cached data that was obtained between January 29 and February 25. This will force the calculator to pick up new data if it cached bad data while the API was broken. If anyone is still having problems, please let me know.