## How Often Does Friday the 13th Happen?

#### Background

So yesterday was Friday the 13th.

I hadn’t even thought anything of it until someone mentioned it to me. They also pointed out that there are two Friday the 13ths this year: the one that occurred yesterday, and there will be another one in October.

This got me to thinking: how often does Friday the 13th usually occur? What’s the most number of times it can occur in a year?

Sounds like questions for a nice little piece of everyday analytics.

#### Analysis

A simple Google search revealed over a list of all the Friday the 13ths from August, 2010 up until the end of 2050 over at timeanddate.com. It was a simple matter to plunk that into Excel and throw together some simple graphs.
So to answer the first question, how often does Friday the 13th usually occur?
It looks like the maximum number of times it can occur per year is 3 (those are the years Jason must have a heyday and things are really bad at Camp Crystal Lake) and the minimum is 1. So my hypothesis is:
a. it’s not possible to have a year where a Friday the 13th doesn’t occur, and
b. Friday the 13th can’t occur more than 3 times in a year, due to the way the Gregorian calendar works.
Of course, this is not proof, just evidence, as we are only looking at a small slice of data.
So what is the distribution of the number of unlucky days per year?
The majority of the years in the period have only one (18, or ~44%) but not by much, as nearly the same amount have 2 (17, or ~42%). Far less have 3 F13th’s, only 6 (~15%). Again, this could just be an artifact of the interval of time chosen, but gives a good idea of what to expect overall.
Are certain months favoured at all, though? Does Jason’s favourite day occur more frequently in certain months?
Actually it doesn’t really appear so – they look to be spread pretty evenly across the months and we will see why this is the case below.
So, what if we want even more detail. When we say how frequently does Friday the 13th occur, and we mean how long is it between each occurrence of Friday the 13th? Well, that’s something we can plot over the 41-year period just by doing a simple subtraction and plotting the result.
Clearly, there is periodicity and some kind of cycle to the occurrence of Friday the 13th, as we see repeated peaks at what looks like 420 days and also at around 30 days on the low end. This is not surprising, if you think about how the calendar works, leap years, etc.
If we pivot on the number of days and plot the result, we don’t even get a distribution that is spread out evenly or anything like that; there are only 7 distinct intervals between Friday the 13ths during the period examined:
So basically, depending on the year, the shortest time between successive Friday the 13ths will be 28 days, and the greatest will be 427 (about a year and two months), but usually it is somewhere in-between at around either three, six, or eight months. It’s also worth noting that every interval is divisible by seven; this should not be surprising at all either, for obvious reasons.

#### Conclusion

Overall and neat little bit of simple analysis. Of course, this is just how I typically think about things, by looking at data first. I know that in this case, the occurrence of things like Friday the 13th (or say, holidays that fall on a certain day of week or the like) are related to the properties of the Gregorian calendar and follow a pattern that you could write specific rules around if you took the time to sit down and work it all out (which is exactly what some Wikipedians have done in the article on Friday the 13th).
I’m not a superstitious, but now I know when those unlucky days are coming up and so do you… and when it’s time to have a movie marathon with everyone’s favourite horror villain who wears a hockey mask.

## How to Export Your Outlook Inbox to CSV for Data Analysis

So one of my colleagues at work showed me this cool script he wrote in Visual Basic to pull all the data from Outlook for analysis.

Cool, I thought – I’d like to do that, but don’t want to muck about in VB.

Well, I was surprised to discover that Outlook has the ability to export email to CSV built in! Follow the simple steps below (here demonstrated in Outlook 2010) and you can analyze your emails yourself and do some cool quantified self type analysis

#### How to Export Outlook Email to CSV (from Outlook)

1. Open Outlook and click File then Options to bring up the options dialog:
2. Selected Advanced, then click the Export button:
3. Click Export to a file and then the next button:
4. Selected Comma Separated Values (Windows) and click next.
5. Unless you want to export a different folder, select Inbox and click next.
6. Browse to a folder and/or type a filename for your export.
7.  Choose Map Custom Fields… if you want to customize which fields to export. Otherwise click the Finish button.
8. Sit tight while Outlook does its thing.
You should now have a CSV file of your inbox data!

#### How to Export Outlook Email to CSV (from Access)

This is all very well and good, but unfortunately exporting to CSV from Outlook does not provide the option for date and time as fields to be included, which makes it useless if you’d like to do time series (or other temporal) analysis.
To get the date and time data you can pull data from Outlook into Access and then export it as noted in this metafilter thread.
Import from Outlook into Access
1. Fire up Access and create a new database. Select External Data, More.. and then Outlook Folder.
2. Select Import the source data into a new table in the current database and click OK

3. Select the email account and folder you’d like to import and click Next
4. Change the field settings if you’d like. Otherwise accept the defaults by clicking Next

5. Let Access add the primary key or not (you don’t need it). Click Next

6. Click Finish and wait. When the process is done you should have a new table called ‘Inbox’.

Export Data from Access to a CSV
1. Make sure the Inbox table is selected and click External Data then Text File.
2. Pick or type a filename and click OK

3. Selected Delimited and click Next
4. Select Comma as the delimiter and tick the box which says Include Field Names on First Row. Click next.
5. Pick or type a filename and click Finish

You should now have your Inbox data exported as CSV (including time / date data!) and ready for analysis. Of course you can repeat this process and append to the Access database folder by folder to analyze all the mail you have in Outlook.