You might be tempted to highlight particular cells with suspicious data, or rows that should be ignored. Instead, add another column with an indicator variable (for example, "trusted", with values TRUE or FALSE).

Here’s an example in which a cell with a suspicious entry is highlighted.

It would be better to include an additional column that indicates the outliers. The highlighting is nice visually, but it’s hard to grab that information for use in the later analysis.

Here’s an example with males highlighted in blue and females in pink. Rather than use highlighting to indicate sex, it’s better to include a sex column, with values Male or Female.

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Next up: Choose good names for things.

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