Rob Wiblin

I saw on your website that you have this kind of table summarizing the evidence on SMS reminders.

And I

I took a quick look over and it seemed like there was five trials that had kind of positive effects and then five where it didn't really seem like the SMS reminders had moved the needle very much.

Did you go away and kind of either yourself or get someone else to do this kind of literature review to learn like other lessons about under what circumstances these things work and like what things you can vary about the intervention to make them have a bigger impact?

Yeah, I was really happy to see the table that both had studies with positive results and studies with no results where it couldn't find an effect.

Because an intervention, even one that's effective, you should find some studies that by chance have found that it didn't work in this particular case or perhaps were underpowered.

There weren't enough people in the sample to detect even a real effect.

And if people aren't aware of that when they're setting out, it suggests that they haven't really been quite comprehensive enough in looking at all of the evidence out there to get a proper average kind of effect size across the full range of results rather than just cherry picking a few of them.

Yeah.

So were there any studies that didn't find an effect where it was possible to kind of identify that some particular thing had been important?

You were suggesting, for example, literacy might mediate the effect of the messages.

If people can't read them, then that's going to reduce the effect size pretty substantially.

Yeah, there are other factors that you had to think about, about whether that would work in your specific context.

Yeah.

This is a bit of a demanding question to know off the top of your head, but maybe to give listeners a sense of kind of the funnel here.

If you were to spend an extra $1,000 scaling up the program, how many SMS messages might you be able to send?

And maybe how many parents would you be able to hassle through this gossip mechanism?

Okay, so something like $20 per additional child immunized or reaching the full immunization schedule.

And is it possible to give a rough approximation of how many lives that will save or how many children you have to get extra vaccinations in order to save a life?

Yeah, the numbers are always changing.