# Dichotomizing when variable is skewed

I have a meeting frequency variable and I want to determine whether it has an effect on hypothesized relationship, by 1) controlling for it and 2)examining whether it is a moderator. Unfortunately, it wasn't a very sensitive measure and distribution is skewed. The breakdown is: 10% daily, 5% twice a week, 52% weekly, 27% fortnightly and 6% monthly.

Someone suggested that because of the distribution (52% in a single category), I wouldn't get anything meaningful out of using it as a ordinal/likert variable. They said, instead, I should dichotomize it as weekly or more (67%) or less than weekly (33%).

I'm unclear on whether or not I should do this. The articles I have read on dichotomizing variables (e.g. MacCallum et al., 2002) say that it is only okay to dichotomize when "the distribution of a count variable is extremely highly skewed". Meeting frequency is skewed (standardised skewness = ~-2), but it is not extremely highly skewed.

Thoughts? I'm thinking at the moment, I'm better off treating it like a likert variable, and then in the limitations section of discussion saying that the variable had low variance and was not very sensitive and this limits the validity of the findings.

Any assistance on this would be great.

The article I read about this is: On the practice of dichotomization of quantitative variables. MacCallum, Robert C.; Zhang, Shaobo; Preacher, Kristopher J.; Rucker, Derek D. Psychological Methods, Vol 7(1), Mar 2002, 19-40

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It would help to draw useful answers if you could describe the ways in which you are controlling for this variable or using it as a moderator. In what sorts of procedures, and with what sorts of other variables? –  rolando2 Oct 6 '12 at 12:49
I am examining how meeting frequency affects the relationship between leader psychological capital and follower psychological capital. So, for moderating: if the leader and the follower meet more frequency does the leaders psychological capital have a stronger relationship with follower psychological capital? For controlling: when controlling for meeting frequency, what is the relationship between leader and follower psychological capital. –  Gabe Oct 7 '12 at 6:17

I think the advice you got is wrong.

First, it's rather strange to think of the skewness of a variable that is ordinal and has 5 categories. Skewness implies interval level data; your scale is not interval level as it stands, but you could make it so by converting it into "times per month met" then daily = 30, twice a week = 8, weekly = 4, fortnightly = 2 6% monthly = 1.

But dichotomizing the data makes "monthly" the same as "weekly" and "daily" the same as "twice a week". These aren't the same. Also, dichotomizing differently (e.g. putting "weekly" with "daily" and "2x a week" might give very different results. That can't be a good thing.

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