8 Style guide

Style guide in the research project life cycle

Figure 8.1: Style guide in the research project life cycle

A style guide provides general agreed upon rules for the formatting of information161. As mentioned in the previous chapter, style guides can be created to standardize procedures such as variable naming, variable value coding, file naming, file versioning, file structure, and even coding practices.

The benefits for creating style guides and using them consistently include:

  • Creating standardization (within and across projects)
  • Improving interpretation: Consistent and clear structure, naming, and coding allows your files and variables to be findable and understandable to humans and computers.
  • Increasing reproducibility: If the organization of your file paths, file naming, or variable naming constantly change it undermines the reproducibility of any data management or analysis code you have written.

Style guides can be created for individual projects, but they can also be created at the team level, to be applied across all projects. Most importantly, they should be created before a project kicks off so you can implement them as soon as your project begins. If you do not have a team-wide style guide already created, you most likely will want to create a project-level style guide during your planning phase so that you can begin setting up your directory structures and file naming standards before you start creating and saving project-related files.

Style guides can be housed in one large document, with a table of contents used to reference each section, or they can be created as separate documents. Either way, style guides should be stored in a central location that is easily accessible to all team members (such as a team or project wiki), and all team members should be trained, and periodically retrained, on the style guide to ensure adherence to the rules. If all team members are not consistently implementing the style guide, then the benefits of the guide are lost.

For the remainder of this chapter, we will spend time reviewing some good practices for rules to add to your style guides for the following purposes:

  1. Structuring directories
  2. Naming files
  3. Naming variables
  4. Assigning variable values
  5. Styling your syntax files

While some best practices will be provided below, ultimately the rules you choose to add to each style guide should be chosen based on which practices work best for your projects and your team. Whatever rules you settle on, write them in a style guide so that everyone is following the same rules within and across projects.

8.1 General good practices

Before we dive in to particular types of style guides, there are a few things to understand about how computers read names in order to understand the “why” behind some of these practices.

  1. Avoid spaces.
    • While some applications (like Windows) recognize spaces, command line operations and some operating systems still do not support them so it is best to avoid them all together. Furthermore, they can often break a URL when shared
    • The underscore _ and hyphen - are good delimiters to use in place of spaces
      • It is worth noting that _ can be difficult to read when file paths are shared in links that are underlined to denote that the path is clickable (for example when sharing a SharePoint link to a document)
  2. With the exception of _ and -, avoid special characters
    • Examples include but are not limited to ?, ., *, \, /, +, ', &, "
    • Computers assign specific meaning to many of these special characters
  3. There are several existing naming conventions that you can choose to add to your style guide. Different naming conventions may work better for different purposes. Using these conventions help you to be consistent with both delimeters and capitalization which not only makes your names more human-readable but also allows your computer to read and search names easier.
    • Pascal case (ScaleSum)
    • Snake case (scale_sum)
    • Camel case (scaleSum)
    • Kebab case (scale-sum)
    • Train case (Scale-Sum)
  4. Character length matters. Computers are unable to read names that surpass a certain character length. This applies to file paths, file names, and variable names. Considerations for each type of limit are reviewed below.

8.2 Directory structure

When deciding how to structure your project directories (the organization of your operating systems folders and files), there are several things you want to consider.

When structuring your folders:

  • First, consider organizing your directory into a hierarchical folder structure to clearly delineate segments of your projects and improve searchability
    • The alternative to using a folder structure is using metadata and tagging to organize and search for files162
  • When creating your folder structure, strike a balance between a deep and shallow structure
    • Too shallow leads to too many files in one folder which is difficult to sort through
    • Too deep leads to too many clicks to get to one file, plus file paths can max out with too many characters. A file path includes the full length of both folders and file names
      • An example file path with 69 characters W:\team\project\data\wave1\student\survey\projecta-w1-stu-svy-raw.csv
    • Examples of file path limits:
      • SharePoint/OneDrive path limit is 400 characters163
      • Windows path limit is 260 characters164
  • Create folders that are specific enough that you can limit access
    • For example you will want to limit user access to folders that hold Personally Identifiable Information (PII)
    • To protect any files that you don’t want others to accidentally edit (for example your clean datasets), also consider making some files “read only”
  • Decide if you want an “archive” folder to move old files into or if you want to leave previous versions in the same folder

When naming your folders:

  • Consider setting a character limit on folder names (again to reduce problems with hitting path character limits)
  • Make your folder names meaningful and easy to interpret
  • Never use spaces in your folder names
    • Use _ or - to separate words
  • With the exception of - and _, don’t use special characters in your folder names
  • Be consistent with delimiters and capitalization. Follow an existing naming convention (as mentioned above).

Example directory structure style guide

1. All project directories follow this hierarchical metadata structure  
    - Level 1: Name of project  
    - Level 2: Life cycle folders  
    - Level 3: Data collection wave folders (if relevant)  
    - Level 4: Participant folder (if relevent)
    - Level 5: Specific content folder  
    - Level 6: Archive folders  
2. All folders should be named according to these rules  
    - Meaningful name but no longer than 20 characters  
    - No spaces or special characters in folder names  
    - Only use lower case letters  
    - Use `-` to separate words  
3. All previous versions of files must be placed into their respective "archive" folder
    - A changelog should be placed in each "archive" folder to document changes between document versions

Example directory structure created using a style guide

1  project-new                          
2   ¦--intervention                     
3   ¦   °--cohort-1                     
4   ¦       °--coaching_materials       
5   ¦           °--archive              
6   ¦               °--changelog.txt    
7   ¦--project-mgmt                     
8   ¦   °--cohort-1                     
9   ¦       °--scheduling-materials     
10  ¦           °--archive              
11  ¦               °--changelog.txt    
12  ¦--documentation                    
13  ¦   ¦--sops                         
14  ¦   ¦   °--archive                  
15  ¦   ¦       °--changelog.txt        
16  ¦   °--data-dictionaries            
17  ¦       °--archive                  
18  ¦           °--changelog.txt        
19  ¦--data                             
20  ¦   °--cohort-1                     
21  ¦       °--student                  
22  ¦           °--survey               
23  ¦               °--archive          
24  ¦                   °--changelog.txt
25  °--tracking                         
26      °--cohort-1                     
27          ¦--participant-database     
28          ¦   °--archive              
29          ¦       °--changelog.txt    
30          °--parent_consents          

8.3 File naming

xkcd comic on naming files

Figure 8.2: xkcd comic on naming files

As xkcd165 so aptly points out in Figure 8.2, many of us are pretty bad at naming files in a consistent and usable way. We are often in a rush to save our files and maybe don’t consider how unclear our file names will be for future users (including ourselves).

Our file names alone should be able to answer questions such as:

  • What are these documents?
  • When were these documents created?
  • Which document is the most recent version?

A file naming style guide helps us to name files in a way that allows us to answer these questions. You can have one overarching file naming guide, or you may have file naming guides for different purposes that need different organizational strategies (for example one naming guide for project meeting notes, another naming guide for project data files). Let’s walk through several conventions to consider when naming your files.

  • Make names descriptive (a user should be able to understand the contents of the file without opening it)
  • Never use spaces between words
    • Use - or _ to separate words.
  • With the exception of _ and -, never use special characters
  • Be consistent with delimiters and capitalization. Follow an existing naming convention.
  • Consider limiting the number of allowable characters to prevent hitting your path limit (as mentioned above)
  • Do not use / in dates and format them consistently. It is beneficial to format dates using the ISO 8601 standard in one of these two ways:
    • While the first way adds more characters to your variable names, it also may be clearer for users to interpret. Either of these date formats will be sortable.
  • When versioning your files, pick a format and add it to your style guide
    • If you plan to version using a number, consider left padding with 0 before single digit numbers to keep the file name the same length as it grows (v01, v02).
    • As mentioned in our chapter on Documentation, it is possible to version programatically using tools like Git and GitHub. However, these tools are not always practical for education research. A more practical means of versioning may be to manually version files and track changes in a changelog.
  • If your files need to be run in a sequential order, add the order number to the beginning of the file name, with leading zeros to ensure proper sorting (01_, 02_)
  • Choose abbreviations and/or consistent terms to use for common names/phrases and add them to your style guide (student = stu).
    • This helps reduce file name character lengths and also creates standardized, searchable metadata, which can allow you to more easily, programmatically retrieve files (for example, retrieve all files containing the phrase “stu_obs_raw”).
  • Keep redundant metadata in the file name
    • This reduces confusion if you ever move a file to a different folder or send a file to a collaborator. It also makes your files searchable.
    • For example, always put the data collection wave in a file name, even if the file is currently housed in a specific wave folder. Or always put the project name in the file name, even if the file is currently housed in a project folder.
  • Choose an order for file name metadata (ex: project -> time -> participant -> measure)

Example file naming style guide

1. Never use spaces between words
2. Never use special characters
3. Use _ to separate words
4. Only use lower case letters
5. Keep names under 35 characters
6. Use the following metadata file naming order:
  - Order of use (if relevant–and always add a 0 before single digits)
  - Project
  - Cohort/Wave (if relevant)
  - Participant
  - Measure
  - Further description
  - Date (always add)
  - Version (if necessary)
7. Format dates as YYYY-MM-DD
8. If there are multiple versions of a document on the same date, version using v# with a leading 0.
9. Use the following abbreviations
  - student = stu
  - survey = svy
  - wave = w
  - project math efficacy = me

Example file names created using a style guide


8.4 Variable naming

This style guide will be a necessary document to have before you start to create your data dictionaries. Below are several considerations to review before developing your variable naming style guide. These are broken into two types of rules, those that are non-negotiable requirements that really should be included in your style guide (if you do not follow these rules you will run into serious problems in interpretation for both humans and machines), and then best practices suggestions that are recommended but not required.


  • Don’t name a variable any keywords or functions used in any programming language (such as if, for, repeat)166
  • Set a character limit
    • Most statistical programs have a limit on variable name characters
      • SPSS is 64
      • Stata is 32
      • SAS is 32
      • Mplus is 8
      • R is 10,000
    • With this said, do not limit yourself to 8 characters based on the fact that one future user may use a program like Mplus. Consider the balance between character limit and interpretation. It is very difficult to make good human-readable variable names under 8 characters. It is much easier to make them under 32. And the majority of your users will be using a program with a limit of 32 or more. If you have one potential Mplus user, they can always rename your variables for their specific analysis.
  • Use the same variable name across time in a project
    • If an item is named anx1 in the fall, name that same item anx1 again in the spring
  • Don’t use spaces or special characters (except_), they are not allowed in most programs
    • Even the - is not allowed in programs such as R and SPSS as it can be mistaken for a minus sign
    • While . is allowed in R and SPSS it is not allowed in Stata so it’s best to avoid using it
  • Do not start a variable name with a number. This is not allowed in many statistical programs.
  • All variable names should be unique
    • This absolutely applies to variables within the same dataset, but it should also apply to all variables across datasets within a project. The reason is, at some point you may merge data across forms and end up with identical variable names (which programs will not allow).
    • So, for example if you collect student gender from a survey and you also collect student gender from school records, differentiate between the two (s_gender and d_gender)
  • If you substantively change an item (substantive wording OR response options change) after at least one round of data has been collected, version your variable names in order to reduce errors in interpretation.
    • For example revised anx1 becomes anx1_v2


  • Names should be meaningful
    • Instead of naming gender q1, name it gender
    • If a variable is a part of a scale, consider using an abbreviation of that scale plus the scale item number (anx1, anx2, anx3)
      • Not only does this allow you to easily associate an item with a scale, but it also allows you to programatically select and manipulate scale items (for example, sum all items that start with “anx”)
  • If you have used the question/scale before, consider keeping the variable name the same across projects. This can be very useful if you ever want to combine data across projects.
  • Be consistent with delimiters and capitalization. Follow an existing naming convention.
    • Snake case (scale_sum) – preferred method for variable names
    • Kebab case (scale-sum) – don’t use for variable names
    • Train case (Scale-Sum) – don’t use for variable names
  • Consider denoting reverse coding in the variable name to reduce confusion (anx1_r)
  • Choose abbreviations and standard phrases to use across all variables. Using controlled vocabularies improves interpretation and also makes data exploration and manipulation easier167.
    • mean = mean
    • scaled score = ss
    • percentile rank = pr
  • Include an indication of the measure in the variable name (for example as a prefix) so you always know what instrument the item came from. This can also help with the unique variable name requirement above.
    • s = student self-report
    • t = teach report on students
    • s_anx1, t_conf2

Example variable naming style guide

1. Use snake case
2. Keep names under 32 characters
3. Use meaningful variable names
4. If part of a scale, use scale abbreviation plus item number from the scale (not order number)
5. Include an indication of the measure as a prefix in the variable name
  - student self-report survey = s_
  - teacher self-report survey = t_
  - district student level data = d_
6. Denote reverse coded variables using suffix `_r`

Example variable names created using a style guide


8.4.1 Time

Before moving on there is one last consideration for variable names. If your data is longitudinal, you may need to add rules for accounting for time in your variable names as well.

Depending on how you plan to combine your data over time, there are two different ways to account for time.

  1. Concatenate time to your variable names. You do this if you plan to merge your data across time in wide format. The reason you need to concatenate time to your variable names here is because your variable names will repeat (anx1 in wave 1, anx1 in wave 2). And remember from our guidelines above, all variable names in a dataset must be unique. In order to create unique variable names and correctly interpret when items were given, we add time to our variable names. The only variables you will not assign time to are your linking variables (such as student unique identifier, teacher unique identifier, and so on). Those variables need to stay identical for linking purposes and will only appear once in your data after merging.
  2. Create time variables and add them to your data. You do this if you plan to append your data over time in long format. Appending your data in long format requires no additional work in terms of variable naming. As discussed in our data structure chapter, you actually want your variables to be identically formatted and named across time when appending. So here, in order to differentiate when items were asked, we add a new variable such as time or wave and add the appropriate value for each row.

During an active project, it is actually best to not combine data and to store all datasets as distinct files until you are either ready to internally use your data or you are ready to publicly share your data (during the preparing for archiving phase). At that time you can make a decision on the best way to combine your data (if you need to combine them at all), and programatically add time to variable names (if necessary).168 Waiting to combine data has benefits:

  1. Having variables named consistently over time (with no time component added) allows you to easily reuse your data collection and data capture tools, as well as your cleaning code, each wave.
  2. Storing files separately prevents you from potentially wasting time combining your data in a way that ends up not actually being useful or from wasting time merging datasets that later need to be re-combined because you find an error in an individual dataset at some point. Time in variable names

While combining your datasets across time should not happen early on in your project, it is helpful to consider early on how you might combine data in the future. If you do plan to potentially merge data in a wide format, it can be helpful to go ahead and plan your rule for adding time to variable names, and add that rule to your style guide. Just be abundantly clear in your guide that this time component should only be added when datasets are combined.

There is no right or wrong way to assign time in your variable names necessarily. Just make sure you continue to follow the rules from above (such as never starting a variable name with a number). Below are some options for adding time to a sample variable, s_gender.

  • As a prefix or suffix with a generic abbreviation, such as w1 for wave 1, added with a delimiter _
    • w1_s_gender or s_gender_w1
  • As a prefix or suffix with a meaningful abbreviation, such as f21 for fall 2021, added with a delimiter (_)
    • f21_s_gender or s_gender_f21
  • One of the above options with no delimiter
    • w1s_gender or s_genderw1
  • As a number embedded into your variable at a certain location, for instance, after an existing prefix such as s for student survey
    • s1_gender, s2_gender

While the first and second method do add additional characters to your variable name, there are also benefits to adding time in these ways. First, it can be easier to visually spot and interpret the time component when it is separated with a delimiter. Second, adding time as a standalone component also allows you to more easily, programmatically, manipulate the time component of your variable. This gives you more flexibility in working with your data, especially in selecting variables and restructuring your datasets.

8.5 Value Coding

In addition to naming variables in a standardized way, variables values also need to be added consistently. Value codes apply to any of your categorical variable. This may be numeric categorical values with associated labels (ex: “no” = 1) or it may be character categorical values with associated labels (ex: “no” = ‘n’).

First, if you are using a pre-existing measure, assign values and labels in the manner that the technical documentation tells you to assign codes. That will be important for any further derivations you need to make later on based on those measures. Otherwise, you will be assigning your own values and labels. Some guidelines for assigning codes and labels (as well as examples for how to apply those guidelines) are below.

  • Values must be unique
    • Do: Assign “yes” = 1 and “no” = 0
    • Don’t: Assign “yes” = 1 and “no” = 1
  • Values must be consistent within a variable
    • Do: For gender assign “male” = ‘m’
    • Don’t: For gender allow “male” = ‘m’ or ‘M’ or ‘Male’ or ‘male’
  • Values must be consistent across time
    • Do: Assign anx1 values of “yes” = 1 and “no” = 0 in wave 1 and wave 2
    • Don’t: Assign anx1 values of “yes” = 1 and “no” = 0 in wave 1 and values of “yes” = 1 and “no” = 2 in wave 2
  • Values should be consistent across the project
    • Do: Assign “yes” = 1 and “no” = 0 as the value for all yes/no items
    • Don’t: Assign “yes” = 1 and “no” = 0 for some variables, and “yes” = 1 and “no” = 2 for others
      • Unless a pre-existing measure determines how some variables are coded
  • Order Likert-type scale response options in a logical way
    • Do: Assign “Strongly Disagree” = 1; “Disagree” = 2; “Agree” = 3; “Strongly Agree” = 4
    • Don’t: Assign “Strongly Disagree” = 1; “Disagree” = 3; “Agree” = 4; “Strongly Agree” = 2
      • Unless a pre-existing measure tells you to code variables in a different way
  • Define missing values
    • You may choose to leave all missing values as blank, NA, or NULL and that is okay
    • However, you may care about the specific reason for missing data and need to consider defining missing values based on their properties
      • The key in this case is to use extreme values that do not actually occur in your data and to also use values that match your variable type (ex: numeric missing values for numeric variables)169
Missing values assigned in the ECLS-K:2011 data file

Figure 8.3: Missing values assigned in the ECLS-K:2011 data file

8.6 Coding

If your team plans to clean data using code, it can be very helpful to create a coding style guide. This style guide can be tailored to a specific language that all staff will use (such as R or Stata), or it can be written more generically to apply to any coding language staff use to clean data. Below is a small sampling of good coding practices to consider adding to your guide. If you are looking for guides for a specific language, it can be very helpful to google existing style guides in that language.

  • Consider building and implementing coding templates170
    • Templates can standardize the format of syntax files (such as using standard headers to break up code)
    • They also standardize the summary information provided at the beginning of your syntax (code author, project name, date created)
  • Use comments throughout your code to clearly explain the purpose of each code chunk
    • The format of these comments will be dependent on your coding language
      • R uses #
      • SPSS and Stata use *
  • Improve code readability by using171
    • spaces
    • indentation
    • setting a line limit for your code (ex: 80 characters)
  • Use relative file paths for reproducibility
    • Setting absolute file paths in syntax reduces reproducibility because future users may have different file paths. It is important to set file paths relative the directory you are working in.172
  • If you create objects in your program (like you do in R or Python), consider adding object naming rules similar to variable naming rules
    • No spaces in object names
    • No special characters except _ to separate words
    • No names that are existing program keywords (if, for, etc.)
  • Reduce duplication, improve efficiency, and increase your ability to troubleshoot errors by using functions, loops, or macros for repetitive code chunks
  • Record session information for future users
    • Record both version information as well as operating system information relevant to your code to increase the reproducibility of your code