correlate and pwcorr both calculate correlations. But correlate calculates correlations where all cases included are nonmissing; if one case has missing observation, the entire row is removed from calculation.

. sysuse auto

. corr rep78 mpg price

calculates pairwise correlations among the three variables. rep78 contains missing values; so when calculating the correlation of mpg and price, it only includes the observations where values of rep78 are nonmissing.

```
(obs=69)
| rep78 mpg price
-------------+---------------------------
rep78 | 1.0000
mpg | 0.4023 1.0000
price | 0.0066 -0.4559 1.0000
```

. pwcorr rep78 mpg price if !missing(rep78, mpg, price) does the same thing as above.

```
| rep78 mpg price
-------------+---------------------------
rep78 | 1.0000
mpg | 0.4023 1.0000
price | 0.0066 -0.4559 1.0000
```

However, pwcorr rep78 mpg price, without if !missing(rep78, mpg, price), would include the observations where rep78 has missing values when calculating the correlation of mpg with price.
```
| rep78 mpg price
-------------+---------------------------
rep78 | 1.0000
mpg | 0.4023 1.0000
price | 0.0066 -0.4686 1.0000
```