Supplementary post of data and methods

Supplementary post to "You only have 1.3 years of playtime with your child in your life"

This short post is the supplementary material about data, methods, and assumptions used the the main post: “You only have 1.3 years of playtime with your child in your life”.

I use child age 0-50 as a measure of the whole life we may have with her: if a child was born when we were 20 (or 30 or 40), we would be 70 (or 80 or 90) when they’re 50.

1. Counting hours in childhood (ages 0 – 17)

We anchored the entire model on the 2021 American Time Use Survey (ATUS), the diary‑based study in which thousands of U.S. parents record everything they do in ten‑minute increments for a full day.

• Primary child‑care minutes – time spent directly feeding, bathing, reading, playing, helping with homework.

• Secondary presence minutes – time a parent is awake with the child while doing something else (cooking, folding laundry).

• Leisure & sports minutes – captures true “fun together” (board games, playground, movie night).

ATUS provides figures for age buckets 0‑5, 6‑12, and 13‑17. We linearly interpolated inside each bucket so the curve drops smoothly instead of stepping down in jolts at age 6 and 13.

Key datapoint: parents of a preschooler average 7.0 waking hours together per day; by senior year of high school that’s under 3.5 hours.

2. Hitting the 18‑year cliff (ages 18 – 22)

With no national diary study of college students’ time at home, we built a calendar model from academic calendars and travel data:

Winter break (24 d) + Thanksgiving (5 d) + partial spring break at home (4 d) + weighted summer (40 d after subtracting internships) + long weekends (6 d) = ~79 home‑days for a freshman. Tapers to ~64 days by age 22. Each home‑day credits 6 waking hours engaged.

3. Life in the visiting years (ages 23 – 50)

We triangulated two surveys:

• CDC National Health Interview Survey 2021 – frequency of seeing parents.

• AARP/NORC Adult‑Child Caregiving Study 2019 – about 9 short visits + one 4‑day holiday per year.

Resulting calendar‑day estimates: 5.5 d/year at age 30, drifting to ~3 d/year by age 50. Each visit assumes 6 waking hours together, 60 % counted as leisure.

Interpolation is linear within each five‑year band.

4. From minutes to “lifetime years”

• Daily hours × 365 → annual hours.

• Sum across ages → lifetime hours.

• Divide by 24 → equivalent calendar days.

• Divide by 365 → equivalent years.

Even if every assumption is 20 % off, the first two decades still hold > 90 % of all awake hours together.

5. Conservative by design

• Rounded up visit lengths and assumed everyone gets home for Thanksgiving.

• Credited 6 engaged hours per visit, though many adult visits include errands or screen time.

• Treated secondary presence equal to eye‑level engagement for waking‑hour totals.

References

1. U.S. Bureau of Labor Statistics. American Time Use Survey Microdata, 2021.

2. National Association of Colleges & Employers 2022 Internship Survey.

3. Harvard, Michigan, Texas academic calendars.

4. U.S. DOT Thanksgiving Travel Trends 2019.

5. CDC NHIS 2021.

6. AARP & NORC Caregiving Study 2019.

7. Tim Urban, “The Tail End,” 2015.