« Visually exploring the relationship between college applicants and enrollment | Main | Say it thrice: a nice example of layering and story-telling »


Dave C.

There may also be some seasonality to consider. NHTSA shows a correlation between fatalities and monthly average temperature. April is a month that has school bus traffic as well as people getting on motorcycles and bicycles.
Could you change your graph to compare 4/20 to other days in April and May with similar temperatures?


Dave: Would recommend reading the more detailed report at Harper's site. He and Palayew tried two other set of reference days: going two weeks instead of one week around the analysis day; something they call "all other control days," which I think means the same day of the week in the other 51 weeks. They also compared analyses of April 20 and of July 4. The July 4 effect is much more solid. Doesn't directly address your question but a similar type of analysis.

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been saved. Comments are moderated and will not appear until approved by the author. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Comments are moderated, and will not appear until the author has approved them.

Your Information

(Name is required. Email address will not be displayed with the comment.)


Link to Principal Analytics Prep

See our curriculum, instructors. Apply.
Kaiser Fung. Business analytics and data visualization expert. Author and Speaker.
Visit my website. Follow my Twitter. See my articles at Daily Beast, 538, HBR.

See my Youtube and Flickr.

Book Blog

Link to junkcharts

Graphics design by Amanda Lee

The Read

Keep in Touch

follow me on Twitter