Control Charts and GTD

I wrote this some while back during my eighth week using Todoist as my task tracking software. Every time I pick up a new one, I start over with what I remember from half-heartedly working through David Allen’s Getting Things Done methodology.

It just happens that about four weeks into using Todoist, I started reading the new edition of Allen’s book, and getting back into the habit of using the system. This time, after starting GTD again for the umpteenth time, I wanted to test whether or not I was actually getting more done. At the same time, I’ve a renewed interest in control charts as I caught up on my reading on Deming.

Control charts help measure whether a process is stable. If I look at the number of tasks I complete each day, grouped by week, and how much I get done is about the same week to week, then I have stable output. One of the nice things about control charts is the explicit built in understanding of variability. This helps, because for me, no two days are alike for me, but week-to-week shouldn’t be too different. There may very well be better statistical tools for this task, but I wanted to learn more about control charts and possible application to personal output.

I’m using three different control charts to look at the number of tasks completed everyday (grouped by week), the range of daily tasks (max – min) completed in a week, and the proportion of days that fall outside the expected upper and lower bounds of daily tasks complete.

These upper and lower bounds are calculated, so we need an initial sample set to compare against. Since what I’d really like to know is whether there is a difference in my productivity once I’ve started embracing GTD. In order to do this, I needed before and after data, which I was able to get through the Todoist API.

I have about 3.5 weeks of use of Todoist before getting back onto the GTD bandwagon, so I used the first four weeks as the baseline. You’ll see a dashed vertical line a reminder of four weeks as the before and after mark. We’ll talk through the output of the control graphs from top to bottom.

example control charts
example control charts

Top Chart – Task Completed per Day

Our top chart is the number of tasks accomplished on any given day, grouped in order by week. The solid gray lines represent the calculated upper and lower bounds of the range of the number of tasks I should expect to complete on any day. In control charts, these are called the Upper Control Line (UCL) and Lower Control Line (LCL).

Each of the gray and red dots represents the number of tasks completed in a day of that week. The marks are gray if they fall between the LCL and UCL, and are red if they are outside of them (greater than or less than respectively). I have enough variability in what I accomplish that the LCL is pretty low, so it would have to be a pretty slow day to not exceed it.

The shape of the dots represent whether the portion of the days where tasks complete fall outside of the UCL/LCL range exceeds what’s expected. More on this when we talk about the bottom chart.

The middle dashed line is the average number of tasks across those first four weeks.

The blue line is the average number of tasks for each given week.

What’s My Read of the Top Chart?

Following the pattern of the blue average line, It sure looks to me like my average weekly productivity has increased since implementing GTD. From the number of red dots, I also have more days that exceed the UCL than before, including two consecutive weeks (out of three) with two outstanding days, versus the average of one.

Middle Chart – Range of Tasks Completed per Week

Each point on this chart represents, for the given week, the most tasks completed in a day minus the least tasks completed in a day.

The solid gray lines, like in the top chart, represent the UCL and LCL. Similarly, the dashed horizontal line is the average for the first four weeks, and the dashed vertical line is our before/after demarcation reminder.

What’s My Read of the Middle Chart?

My first full week using GTD, week 5, shows a really big jump in the range. If you look at the top chart for the same week, you can see this is due to one ridiculously task driven day. My calendar doesn’t show anything unusual for the day, but this is the first Monday using GTD after I began the book on the Friday before. I’ll chalk it up to enthusiasm.

The following week, the range decreases a bit, while the average still goes up (top chart). So while the average productivity is still influenced by extremes (here two instead of one), we are seeing a swing closer to average. I’m not sure whether this is increased productivity, or a fluke, but I’d like to see better results due to the process, not from enthusiasm and energy of something new. I hope that what we’re beginning to see.

Oh, and that red mark in week 8, that’s because I only have one day of data. Max – Min = 0, when they’re both the same day.

Bottom Chart – Days Outside the Predicted Range of Completed Tasks by Week

Even when a process is stable, there can still be errors: errors outside of specifications and errors outside of the UCL/LCL. I think this chart is supposed to be errors outside of specification, but since I have no idea what I’d like my spec for productivity to be, I’m using the UCL/LCL in the tasks completed (top chart).

What’s My Read of the Bottom Chart?

I don’t get much more from this chart than discussed in the top chart, but what I’m looking for is more days that exceed the UCL than average. Typically, it’s one day a week. Since starting GTD, I’ve had a couple of high weeks. Let’s hope that’s the beginning of a trend.


While there are a lot of assumptions going into this, like: weeks are similar even when days aren’t, and I’m similarly recording the actions I complete. But, as I use this over a longer period of time, those won’t matter so much.

It’s a fun exercise, but you need a lot of data to get started. I’m glad Todoist has the API, and it looks like I’m off to a promising start on getting more done.