Binomial probabilities by month and age grouping—probabilities of having up to the number of visits observed in each month if visits were distributed equally across months during the study period
| Month of year | Expected percentage of total | Age 0–18 years | Age 5–18 years | Age 13–18 years | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Observed frequency | Expected frequency* | Cumulative binomial probability† | Observed frequency | Expected frequency* | Cumulative binomial probability† | Observed frequency | Expected frequency* | Cumulative binomial probability† | ||
| January | 8.33 | 310,000 | 269,000 | 0.995 | 306,000 | 253,000 | 1.0 | 183,000 | 157,000 | 0.985 |
| February | 8.33 | 250,000 | 269,000 | 0.119 | 240,000 | 253,000 | 0.199 | 148,000 | 157,000 | 0.243 |
| March | 8.33 | 227,000 | 269,000 | 0.003 | 225,000 | 253,000 | 0.032 | 157,000 | 157,000 | 0.524 |
| April | 8.33 | 223,000 | 269,000 | 0.001 | 210,000 | 253,000 | 0.002 | 152,000 | 157,000 | 0.360 |
| May | 8.33 | 254,000 | 269,000 | 0.178 | 245,000 | 253,000 | 0.304 | 150,000 | 157,000 | 0.299 |
| June | 8.33 | 284,000 | 269,000 | 0.838 | 251,000 | 253,000 | 0.454 | 141,000 | 157,000 | 0.098 |
| July | 8.33 | 230,000 | 269,000 | 0.006 | 206,000 | 253,000 | 0.001 | 96,000 | 157,000 | <0.001 |
| August | 8.33 | 294,000 | 269,000 | 0.946 | 271,000 | 253,000 | 0.882 | 154,000 | 157,000 | 0.425 |
| September | 8.33 | 350,000 | 269,000 | 1.0 | 336,000 | 253,000 | 1.0 | 225,000 | 157,000 | 1.0 |
| October | 8.33 | 333,000 | 269,000 | 1.0 | 316,000 | 253,000 | 1.0 | 206,000 | 157,000 | 1.0 |
| November | 8.33 | 221,000 | 269,000 | <0.001 | 208,000 | 253,000 | 0.001 | 143,000 | 157,000 | 0.131 |
| December | 8.33 | 253,000 | 269,000 | 0.162 | 228,000 | 253,000 | 0.049 | 129,000 | 157,000 | 0.010 |
| Total | 3,228,000‡ | 3,228,000 | 3,041,000‡ | 3,036,000§ | 1,883,000‡ | 1,884,000§ | ||||
All entries are rounded to the nearest thousand.
*Total observed divided by 12; included for reference only.
†Cumulative probability that the actual number of headaches is less than or equal to the observed number with the given expected percent in the total number of trials.
‡Total of months does not equal point estimate due to rounding.
§Total expected does not equal total observed due to rounding.