<p>It is reasonable to show both observations and number of units of analysis. For instance, take <a href="http://economics.mit.edu/files/5677" rel="nofollow noreferrer">this example</a> of an article in the American Economic Review:</p>

<p><a href="https://i.sstatic.net/6aAAI.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6aAAI.png" alt="enter image description here"></a></p>

<p>There is the row <strong>Observations</strong>, and the row <strong>Countries</strong>. The latter is the unit of analysis. As the data is a longitudinal panel, there are multiple observations per country. As the panel is unbalanced, the number of observations is generally not a multiple of the number of countries (e.g. for Pooled OLS (column 1), $945/150=6.3$).</p>

CC BY-SA 3.0
2017-03-15T13:10:39.430Z
2017-03-15T13:10:39.430Z
luchonacho
<p>It is conventional to report both the total number of <strong>observations</strong> (1000 in your case) and the number of <strong>groups</strong> (500 in your case). If you want or are allowed to report only one number as the number of <strong>observations</strong>, it is suitable to report 1000 for POLS because POLS doesn't mind the fact that it is a panel data set. For FD, it is slightly confusing to me to say that the number of observations is 500. I would probably ask again of the writer what 500 means.</p>

CC BY-SA 3.0
2017-03-09T22:54:55.683Z
2017-03-09T22:54:55.683Z
chan1142
<p>Given a balanced two-period panel data, with lets say 1000 observations on 500 individuals.</p>

<p>When you estimate a pooled OLS regression and first-differences regression is there a standard in the economics literature on how you should report number of observations. </p>

<p>It seems most natural for me to report 500 observations in the case of first-differences.</p>

<p>This might seem trivial. But better follow any standard if it exists.</p>

CC BY-SA 3.0
2017-03-09T16:33:54.623Z
I don't see how this could be reported as anything other than 500 observations. If you ran a fixed effects regression it would be 1,000 observations but would also have 500 more parameters.
BKay
<econometrics>
Number of observations in different panel data regressions
snoram
# Number of observations in different panel data regressions

(Asked by: username_0 on 2017-03-09)

Given a balanced two-period panel data, with lets say 1000 observations on 500 individuals.

When you estimate a pooled OLS regression and first-differences regression is there a standard in the economics literature on how you should report number of observations.

It seems most natural for me to report 500 observations in the case of first-differences.

This might seem trivial. But better follow any standard if it exists.

**Tags:** econometrics
> **Comments:**
> **username_1**: I don't see how this could be reported as anything other than 500 observations. If you ran a fixed effects regression it would be 1,000 observations but would also have 500 more parameters.  

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## 2 answers

### Answer by username_2 on 2017-03-15. Score: 1 | Accepted answer

It is reasonable to show both observations and number of units of analysis. For instance, take [this example](http://economics.mit.edu/files/5677) of an article in the American Economic Review:

[![enter image description here](https://i.sstatic.net/6aAAI.png)](https://i.sstatic.net/6aAAI.png)

There is the row **Observations**, and the row **Countries**. The latter is the unit of analysis. As the data is a longitudinal panel, there are multiple observations per country. As the panel is unbalanced, the number of observations is generally not a multiple of the number of countries (e.g. for Pooled OLS (column 1), $945/150=6.3$).


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### Answer by username_3 on 2017-03-09. Score: 2

It is conventional to report both the total number of **observations** (1000 in your case) and the number of **groups** (500 in your case). If you want or are allowed to report only one number as the number of **observations**, it is suitable to report 1000 for POLS because POLS doesn't mind the fact that it is a panel data set. For FD, it is slightly confusing to me to say that the number of observations is 500. I would probably ask again of the writer what 500 means.


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