Value Labels in IPUMS data

Cautions regarding labelled variables

While labelled variables provide the benefits described above, they also present challenges.

For example, you may have noticed that both of the means calculated above are suspect:

• In the case of AGE_FACTOR, the values have been remapped during conversion and several are inconsistent with the original data.
• In the case of AGE, we have considered all people over 90 to be exactly 90, and all people over 99 to be exactly 99—labelled variables don’t ensure that calculations are correct any more than factors do!

Furthermore, many R functions ignore value labels or even actively remove them from the data:

ipums_val_labels(cps$HEALTH)
#> # A tibble: 5 × 2
#>     val lbl      
#>   <int> <chr>    
#> 1     1 Excellent
#> 2     2 Very good
#> 3     3 Good     
#> 4     4 Fair     
#> 5     5 Poor

HEALTH2 <- ifelse(cps$HEALTH > 3, 3, cps$HEALTH)

ipums_val_labels(HEALTH2)
#> # A tibble: 0 × 2
#> # ℹ 2 variables: val <dbl>, lbl <chr>

So, labelled vectors are not intended for use throughout the entire analysis process. Instead, they should be used during the initial data preparation process to convert raw data into values that are more meaningful. These can then be converted to other variable types (often factors) for analysis.

Unfortunately, this isn’t a process that can typically be automated, as it depends primarily on the research questions the data will be used to address. However, ipumsr provides several functions to manipulate value labels to make this process easier.

Convert labelled values to other data types

Use as_factor()¹ once labels have the correct categories and need no further manipulation. For instance, MONTH already has sensible categories, so we can convert it to a factor right away:

ipums_val_labels(cps$MONTH)
#> # A tibble: 12 × 2
#>      val lbl      
#>    <int> <chr>    
#>  1     1 January  
#>  2     2 February 
#>  3     3 March    
#>  4     4 April    
#>  5     5 May      
#>  6     6 June     
#>  7     7 July     
#>  8     8 August   
#>  9     9 September
#> 10    10 October  
#> 11    11 November 
#> 12    12 December
cps$MONTH <- as_factor(cps$MONTH)

as_factor() can also convert all labelled variables in a data frame to factors at once. If you prefer to work with factors, you can do this conversion immediately after loading data, and then prepare these variables using techniques you would use for factors.

cps <- as_factor(cps)

# ... further preparation of variables as factors

If you prefer to handle these variables in labelled format, you can use the lbl_* helpers first, then call as_factor() on the entire data frame.

Some variables may be more appropriate to use as numeric values rather than factors. In these cases, you can simply remove the labels with zap_labels().

INCTOT, which measures personal income, fits this description:

inctot_num <- zap_labels(cps$INCTOT)

typeof(inctot_num)
#> [1] "double"

ipums_val_labels(inctot_num)
#> # A tibble: 0 × 2
#> # ℹ 2 variables: val <dbl>, lbl <chr>

Note that labelled values are not generally intended to be interpreted as numeric values, so zap_labels() should only be used after labels have been properly handled. For example, in INCTOT, labelled values used to identify missing values are encoded with large numbers:

ipums_val_labels(cps$INCTOT)
#> # A tibble: 2 × 2
#>         val lbl                      
#>       <dbl> <chr>                    
#> 1 999999998 Missing. (1962-1964 only)
#> 2 999999999 N.I.U.

Treating these as legitimate observations will significantly skew any calculations with this variable if not first converted to NA.

Create missing values based on value labels

Many IPUMS variables use labelled values to identify missing data. This allows for more detail about why certain observations were missing than would be available were values loaded as NA.

As we saw with INCTOT, value labels were used to identify two types of missing data: those that are legitimately missing and those that are not in the universe of observations.

ipums_val_labels(cps$INCTOT)
#> # A tibble: 2 × 2
#>         val lbl                      
#>       <dbl> <chr>                    
#> 1 999999998 Missing. (1962-1964 only)
#> 2 999999999 N.I.U.

To convert one or both of these labelled values to NA, use lbl_na_if(). To use lbl_na_if(), you must supply a function to handle the conversion. The function should take a value-label pair as its input and output TRUE for those pairs whose values should be converted to NA.

# Convert to NA using function that returns TRUE for all labelled values equal to 99999999
inctot_na <- lbl_na_if(
  cps$INCTOT,
  function(.val, .lbl) .val == 999999999
)

# All 99999999 values have been converted to NA
any(inctot_na == 999999999, na.rm = TRUE)
#> [1] FALSE

# And the label has been removed:
ipums_val_labels(inctot_na)
#> # A tibble: 1 × 2
#>         val lbl                      
#>       <dbl> <chr>                    
#> 1 999999998 Missing. (1962-1964 only)

# Convert to NA for labels that contain "N.I.U."
inctot_na2 <- lbl_na_if(
  cps$INCTOT,
  function(.val, .lbl) grepl("N.I.U.", .lbl)
)

# Same result
all(inctot_na2 == inctot_na, na.rm = TRUE)
#> [1] TRUE

lbl_na_if(cps$INCTOT, ~ .val == 999999999)

x <- lbl_na_if(cps$INCTOT, ~ .val >= 0)

# Unlabelled values greater than the cutoff are still present:
length(which(x > 0))
#> [1] 7501

Relabel values

lbl_relabel() can be used to create new value-label pairs, often to recombine existing labels into more general categories. It takes a two-sided formula to handle the relabeling:

• On the left-hand side, use the lbl() helper to define a new value-label pair.
• On the right-hand side, provide a function that returns TRUE for those value-label pairs that should be relabelled with the new value-label pair from the left-hand side.

The function again uses the .val and .lbl syntax mentioned above to refer to values and labels, respectively.

For instance, we could reclassify the categories in MIGRATE1 such that all migration within a state is captured in a single category:

ipums_val_labels(cps$MIGRATE1)
#> # A tibble: 8 × 2
#>     val lbl                                 
#>   <int> <chr>                               
#> 1     0 NIU                                 
#> 2     1 Same house                          
#> 3     2 Different house, place not reported 
#> 4     3 Moved within county                 
#> 5     4 Moved within state, different county
#> 6     5 Moved between states                
#> 7     6 Abroad                              
#> 8     9 Unknown

cps$MIGRATE1 <- lbl_relabel(
  cps$MIGRATE1,
  lbl(0, "NIU / Missing / Unknown") ~ .val %in% c(0, 2, 9),
  lbl(1, "Stayed in state") ~ .val %in% c(1, 3, 4)
)

ipums_val_labels(cps$MIGRATE1)
#> # A tibble: 4 × 2
#>     val lbl                    
#>   <dbl> <chr>                  
#> 1     0 NIU / Missing / Unknown
#> 2     1 Stayed in state        
#> 3     5 Moved between states   
#> 4     6 Abroad

Many IPUMS variables include detailed labels that are grouped together into more general categories. These are often encoded with multi-digit values, where the starting digit refers to the larger category.

For instance, the EDUC variable contains categories for individual grades as well as categories for multiple grade groups:

head(ipums_val_labels(cps$EDUC), 15)
#> # A tibble: 15 × 2
#>      val lbl                 
#>    <int> <chr>               
#>  1     0 NIU or no schooling 
#>  2     1 NIU or blank        
#>  3     2 None or preschool   
#>  4    10 Grades 1, 2, 3, or 4
#>  5    11 Grade 1             
#>  6    12 Grade 2             
#>  7    13 Grade 3             
#>  8    14 Grade 4             
#>  9    20 Grades 5 or 6       
#> 10    21 Grade 5             
#> 11    22 Grade 6             
#> 12    30 Grades 7 or 8       
#> 13    31 Grade 7             
#> 14    32 Grade 8             
#> 15    40 Grade 9

You could use lbl_relabel() to collapse the detailed categories into the more general ones, but you would have to define new value labels for all the categories. Instead, you could use lbl_collapse().

lbl_collapse() uses a function that takes .val and .lbl arguments and returns the new value each input value should be assigned to. The label of the lowest original value is used for each collapsed group. To group by the tens digit, use the integer division operator %/%:

# %/% refers to integer division, which divides but discards the remainder
10 %/% 10
#> [1] 1
11 %/% 10
#> [1] 1

# Convert to groups by tens digit
cps$EDUC2 <- lbl_collapse(cps$EDUC, ~ .val %/% 10)

ipums_val_labels(cps$EDUC2)
#> # A tibble: 14 × 2
#>      val lbl                 
#>    <dbl> <chr>               
#>  1     0 NIU or no schooling 
#>  2     1 Grades 1, 2, 3, or 4
#>  3     2 Grades 5 or 6       
#>  4     3 Grades 7 or 8       
#>  5     4 Grade 9             
#>  6     5 Grade 10            
#>  7     6 Grade 11            
#>  8     7 Grade 12            
#>  9     8 1 year of college   
#> 10     9 2 years of college  
#> 11    10 3 years of college  
#> 12    11 4 years of college  
#> 13    12 5+ years of college 
#> 14    99 Missing/Unknown

Remove unused value labels

Some variables may contain labels for values that don’t appear in the data. Unused levels still appear in factor representations of these variables, so it is often beneficial to remove them with lbl_clean():

ipums_val_labels(cps$STATEFIP)
#> # A tibble: 75 × 2
#>      val lbl                 
#>    <int> <chr>               
#>  1     1 Alabama             
#>  2     2 Alaska              
#>  3     4 Arizona             
#>  4     5 Arkansas            
#>  5     6 California          
#>  6     8 Colorado            
#>  7     9 Connecticut         
#>  8    10 Delaware            
#>  9    11 District of Columbia
#> 10    12 Florida             
#> # ℹ 65 more rows
ipums_val_labels(lbl_clean(cps$STATEFIP))
#> # A tibble: 5 × 2
#>     val lbl         
#>   <int> <chr>       
#> 1    19 Iowa        
#> 2    27 Minnesota   
#> 3    38 North Dakota
#> 4    46 South Dakota
#> 5    55 Wisconsin

Add new labels

As mentioned above, value labels are intended to be used as an intermediate data structure for preparing newly-imported data. As such, you’re not likely to need to add new labels, but if you do, use lbl_add(), lbl_add_vals(), or lbl_define().

lbl_add() takes an arbitrary number of lbl() placeholders that will be added to a given labelled vector:

x <- haven::labelled(
  c(100, 200, 105, 990, 999, 230),
  c(`Unknown` = 990, NIU = 999)
)

lbl_add(
  x,
  lbl(100, "$100"),
  lbl(105, "$105"),
  lbl(200, "$200"),
  lbl(230, "$230")
)
#> <labelled<double>[6]>
#> [1] 100 200 105 990 999 230
#> 
#> Labels:
#>  value   label
#>    100    $100
#>    105    $105
#>    200    $200
#>    230    $230
#>    990 Unknown
#>    999     NIU

lbl_add_vals() adds labels for all unlabelled values in a labelled vector with an optional labeller function. (This can be useful if you wish to operate on a partially labelled vector with a function that requires labelled input, like lbl_relabel().)

# `.` refers to each label value
lbl_add_vals(x, ~ paste0("$", .))
#> <labelled<double>[6]>
#> [1] 100 200 105 990 999 230
#> 
#> Labels:
#>  value   label
#>    100    $100
#>    105    $105
#>    200    $200
#>    230    $230
#>    990 Unknown
#>    999     NIU

lbl_define() makes a labelled vector out of an unlabelled one. Use the same syntax as is used for lbl_relabel() to define new labels based on the unlabelled values:

age <- c(10, 12, 16, 18, 20, 22, 25, 27)

# Group age values into two label groups.
# Values not captured by the right hand side functions remain unlabelled
lbl_define(
  age,
  lbl(1, "Pre-college age") ~ .val < 18,
  lbl(2, "College age") ~ .val >= 18 & .val <= 22
)
#> <labelled<double>[8]>
#> [1]  1  1  1  2  2  2 25 27
#> 
#> Labels:
#>  value           label
#>      1 Pre-college age
#>      2     College age

Once all labelled variables have been appropriately converted to factors or numeric values, the data can move forward in the processing pipeline.