Improve Your Chances of Having Grandchildren with this One Easy Trick!

Tired of your parents pressuring you to have children? These tables will let people know how many children they’d need to have to reasonably expect grandchildren. That doesn’t mean they can blame their kids if they don’t get any grandchildren. They can blame the fates if they had a 99% chance but still didn’t end up with any grandchildren. What’s more important is that they can stop bothering you! Nothing’s guaranteed, but the following table shows the probabilities of having grandchildren based on how many children you have.

If you have one child, you have an 80% chance of having one or more grandchildren and only a 10% chance of having three or more grandchildren. If you have three children, you have a 99% chance of having one or more grandchildren. I’m not saying that people should have more children than they originally intended, but this table should give them some more reasonable expectations than they’ve previously had.

And here’s a simplified table showing how many children you need to have for 90%, 95%, and 99% confidence that you’ll have one or more grandchildren.

For 90% or 95% confidence that you’ll have one or more grandchildren, you need to have two children. For 99% confidence, you’d have to have three children. You could have seven children and still wouldn’t have a 99% probability of having three or more grandchildren.

Input Data Set

It was assumed that 20% of people won’t have children. For those with children, it was assumed that 22% will have one child, 41% will have two children, 24% will have three children, and just under 13% will have between four and 10 children, each number between four and ten being less likely than the previous number. It would not have changed the results of the simulation for families with greater than ten children to be possible. The table below shows the exact probabilities that were used.

Methodology

A Monte Carlo simulation was run with 10,000 rows for 10 iterations. The number of grandchildren per number of children was counted for each simulation and then averaged across iterations. The dataset for children was generated based on the above probability distribution. Then, data for the number of grandchildren were generated using the same probability distribution and a similar methodology.

For families of three or fewer children, each child was assigned his or her number of children based on the same methodology as above. For families of four or more children, the average of three formulas was calculated and multiplied by the number of children, then rounded, to get the number of grandchildren. This is allowable for larger families such as these because, by the central limit theorem, the total fertility rate for large families should approach a normal distribution with the same mean as the total fertility rate for the entire simulation. That is, if the first generation of the simulation was a family with ten children, one could fairly reasonably say that the fertility rate of those children would be close to 1.84, which is the total fertility rate in the U.S., or in this case 1.93, which was what the total fertility ended up being for these simulations.

I hope you’ve found this information useful.

Feel free to ask me about modeling & simulation, genetic genealogy, or genealogical research. And make sure to check out these ranges of shared DNA percentages or shared centiMorgans, which are the only published values that match peer-reviewed standard deviations. That model was also used to make a very accurate relationship prediction tool. Or, try a calculator that lets you find the amount of an ancestor’s DNA you have when combining multiple kits.

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