RERUN
Claim 37

Do parents of two boys or two girls try for a third child more often?

Independent rebuild

The study said parents whose first two children were both boys or both girls were 6.8 points more likely to have a third. The Lab retraced it: ✓ same result. This can still be challenged.

Whose code is this?

Our own small program, run on a public copy of the paper's data: the same 254,654 married women. It isn't the authors' code. Nobody has run it on the real data yet, us included. It was tested only on made-up data with a known answer, and the Lab runs it once forecasting closes.

See the code

Economists use this nudge to a bigger family as a natural experiment, to measure how children change their parents' working lives.

We test one thing: does this code and data give this number? That's not the same as the science being right. The forecast price never changes the verdict.

See the proof
0.068share of families, 0 to 1, the paper says. Counts if between 0.063 and 0.073.
Where the number comes fromdifference (2) - (1) 0.068 (0.002)Table 3 (continued), married women, 1980 census, of the working paper (NBER 5778), read from the page image

The exact claim as posted

Do parents of two boys or two girls go on to have a third child more often? A 1980 US census study found 6.8 points more

Angrist and Evans (American Economic Review, 1998) looked at married women aged 21 to 35 in the 1980 US census with two or more children. When the first two children were both boys or both girls, 41.4% went on to have another child, against 34.6% when they were one boy and one girl: 6.8 percentage points more. This runs our own small program on a public copy of the paper's 254,654 women. The rebuild isn't the authors' code, so a mismatch ends as inconclusive.

RERUNCLAIM #0037

Do parents of two boys or two girls try for a third child more often?

Measured in
share of families, 0 to 1
Paper says
0.068
Counts if
0.063 to 0.073
Lab got
0.0675
VerdictNumbers check out
3a87812133ada0a5f6a7Nov 12, 2026

This can still be challenged

Paper said 0.068. We got 0.0675.

The code and data produced the same result. That doesn't prove the study's method is right.

This slip is the Lab's .

✓ Verified on NEAR. See the contract's history

See the full receipt

  1. People forecast
  2. Forecasting ends
  3. The Lab retraces it
  4. Verdict posted, open to challenge
  5. Winners collect

What we didn't check

  • Whether the sample was fair or large enough.
  • Whether test data leaked into training or tuning.
  • Whether the result holds on new data.
  • Whether the study's method was the right one for its question.
  • Why parents do it. The study only counts births.
  • Whether it still holds today. The data are from 1980.

Reading how the odds moved…

Watch the Lab work

Result posted, can still be challenged
Connecting to the Lab0 entries

No live log was kept for this run. Its receipt below has the log hash and the end of the output.

The evidence

See the full receipt

How much evidence is behind this?

Each step is a tougher test. Only the first one decides who wins the market.

  1. 1. ✓

    The Lab's retrace of the code and data named in the claim

    The Lab retraced the code and data and got a number inside the claim's range. YES wins.

  2. 2. –

    Stress test: does the number depend on luck?

    Fetching the extra runs…

  3. 3. –

    Rebuilt from the description (experimental)

    Fetching the AI's rebuild…

Coming next: a data-leakage check, for the same rows in training and test data, and a maths check on the statistics a paper reports. Neither has run on this claim.

Even all three steps can't prove the science is true. They show how well this result stands up to checking.

Verified

Your browser just re-checked these itself, so you don't have to trust this site.

Checking…

What the Lab retraces

Source
https://doi.org/10.3386/w5778
J. D. Angrist and W. N. Evans; rebuild by the RERUN project, Rebuild: MIT. Data: GPL (R package AER), fetched from Rdatasets, not redistributed.
Code, at this exact version
https://github.com/Maveri-Q/rerun-rebuilds
commit 6b8ba2d5f26fdf4837a71dfffb43b175586424d3
Commands
python3.11
$ python third-child-1998/rebuild.py Fertility.csv > rerun_output.txt && cat rerun_output.txt
Where the result is read
rerun_output.txt using regex same_sex_difference (-?[0-9.]+)
Data files
Fertility.csv
fingerprint ca9be592b79dddbc2f49ff80f45d0dbe31aac4afb57ff88dec57376c3f3e3452
Limits
2 CPU, 4 GB, 15 minutes
3a87812133ada0a5f6a7b1cf3ad2a15907d1945b8fdbe683e392903c02a9e5c3
Show the claim exactly as stored on the blockchain
{"artifact":{"commit":"6b8ba2d5f26fdf4837a71dfffb43b175586424d3","data":[{"path":"Fertility.csv","sha256":"ca9be592b79dddbc2f49ff80f45d0dbe31aac4afb57ff88dec57376c3f3e3452","url":"https://vincentarelbundock.github.io/Rdatasets/csv/AER/Fertility.csv"}],"entrypoint":"python third-child-1998/rebuild.py Fertility.csv > rerun_output.txt && cat rerun_output.txt","output":{"extractor":{"expr":"same_sex_difference (-?[0-9.]+)","type":"regex"},"path":"rerun_output.txt"},"repo_url":"https://github.com/Maveri-Q/rerun-rebuilds","runtime":"python3.11","setup":[]},"metric":{"comparison":"within_tolerance","name":"extra share having another child when the first two are the same sex","reported_value":"0.068","tolerance":{"type":"abs","value":"0.005"}},"private_data":null,"resources":{"cpu":2,"max_minutes":15,"mem_gb":4},"source":{"authors":"J. D. Angrist and W. N. Evans; rebuild by the RERUN project","doi":"10.3386/w5778","license":"Rebuild: MIT. Data: GPL (R package AER), fetched from Rdatasets, not redistributed.","type":"paper","url":"https://doi.org/10.3386/w5778"},"statement":"Angrist and Evans (American Economic Review, 1998) looked at married women aged 21 to 35 in the 1980 US census with two or more children. When the first two children were both boys or both girls, 41.4% went on to have another child, against 34.6% when they were one boy and one girl: 6.8 percentage points more. This runs our own small program on a public copy of the paper's 254,654 women. The rebuild isn't the authors' code, so a mismatch ends as inconclusive.","title":"Do parents of two boys or two girls go on to have a third child more often? A 1980 US census study found 6.8 points more","version":1}

Community notes

Notes are people's own words, kept on the blockchain. They never change a verdict, and the Lab's AI never reads them. Posting costs a little NEAR for storage, and what isn't used comes back.