The color scale hugely amplifies minor differences, see my other comment. In the dataset, 15 years (2000-2014) are represented and the weekly cycle is therefore present. This could have been mitigated by using a 28-year dataset. Here is how often each month started on a given day in the dataset. We don’t have colored text so I used emoji.
01/
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
SUN
2➖
2➖
1🔻
3⚠️
2➖
3⚠️
3⚠️
2➖
2➖
2➖
1🔻
2➖
MON
2➖
1🔻
2➖
2➖
2➖
1🔻
2➖
2➖
3⚠️
3⚠️
2➖
3⚠️
TUE
3⚠️
3⚠️
2➖
3⚠️
3⚠️
2➖
3⚠️
2➖
1🔻
2➖
2➖
1🔻
WED
2➖
2➖
2➖
1🔻
2➖
2➖
1🔻
3⚠️
2➖
3⚠️
2➖
2➖
THU
2➖
2➖
3⚠️
2➖
3⚠️
2➖
2➖
2➖
2➖
1🔻
3⚠️
2➖
FRI
1🔻
3⚠️
2➖
2➖
1🔻
3⚠️
2➖
3⚠️
2➖
2➖
2➖
2➖
SAT
3⚠️
2➖
3⚠️
2➖
2➖
2➖
2➖
1🔻
3⚠️
2➖
3⚠️
3⚠️
Here is how likely any date is to be Monday-Friday in the data (out of 15):
How often Mon-Fri
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
01/08/15/22/29
10🔻
11➖
11➖
10🔻
11➖
10🔻
10🔻
12⚠️
10🔻
11➖
11➖
10🔻
02/09/16/23/30
11➖
12⚠️
12⚠️
10🔻
11➖
11➖
10🔻
11➖
10🔻
10🔻
12⚠️
10🔻
03/10/17/24/31
10🔻
11➖
11➖
10🔻
10🔻
12⚠️
10🔻
11➖
11➖
10🔻
11➖
11➖
04/11/18/25
10🔻
10🔻
11➖
11➖
10🔻
11➖
11➖
10🔻
12⚠️
10🔻
11➖
12⚠️
05/12/19/26
11➖
11➖
10🔻
12⚠️
10🔻
11➖
12⚠️
10🔻
11➖
11➖
10🔻
11➖
06/13/20/27
12⚠️
10🔻
10🔻
11➖
11➖
10🔻
11➖
10🔻
11➖
12⚠️
10🔻
11➖
07/14/21/28
11➖
10🔻
10🔻
11➖
12⚠️
10🔻
11➖
11➖
10🔻
11➖
10🔻
10🔻
You can see for example that August 01/08/15/22/29 is 10-20% more likely to be a workday than other days, which corresponds to the extra births. Feb 29 cannot be read directly from this table; its value is 3 out of 4 (2000: Tue, 2004: Sun, 2008: Fri, 2012: Wed).
As for your question: every month has approximately the same strength of the weekly cycle, it’s just that the prevailing colors in July-September show them the most. August’s is more visible because it does not have the disrupting July 4 and September 11.
The color scale hugely amplifies minor differences, see my other comment. In the dataset, 15 years (2000-2014) are represented and the weekly cycle is therefore present. This could have been mitigated by using a 28-year dataset. Here is how often each month started on a given day in the dataset. We don’t have colored text so I used emoji.
Here is how likely any date is to be Monday-Friday in the data (out of 15):
You can see for example that August 01/08/15/22/29 is 10-20% more likely to be a workday than other days, which corresponds to the extra births. Feb 29 cannot be read directly from this table; its value is 3 out of 4 (2000: Tue, 2004: Sun, 2008: Fri, 2012: Wed).
As for your question: every month has approximately the same strength of the weekly cycle, it’s just that the prevailing colors in July-September show them the most. August’s is more visible because it does not have the disrupting July 4 and September 11.