ch 4 - wiki article for sampling in the field

[kbjarkefur]

https://github.com/worldbank/d4di/blob/f4a26e93cd799657fead5d8a8442889fe9ca7627/chapters/sampling-randomization-power.tex#L184

@mariaruth is it worth mentioning sampling in the field at all here? it can be necessary if no listing exists. for example, survey teams list all the HH in a village and then interview every 10th HH with a random start point. or if going from paper-records that are not available to the study team in advance. not that common, and all best avoided (since it's not reproducible and hard to verify that protocols are followed exactly), but perhaps worth a mention.

@bbdaniels I'd leave it out, maybe in wiki?

---

When wiki article is written link to it in the text