Introduction
Once you have downloaded MCS data from the UK Data Service, you will notice that the data from a given sweep is split across multiple files (e.g., as in the below screenshot). The reason for this is that the MCS contains information on different observational units, for instance on the cohort members, the cohort members’ parents, and the cohort members’ families. The data is split across different files so that it can be stored efficiently. For instance, variables on the cohort members themselves are stored in files with one row per cohort member, while variables on parents are stored in files with one row per parent. The aim of this tutorial is to give you an overview of the data structures used by the MCS.
Naming Conventions
The MCS data files use a consistent naming convention. Files are prefixed mcs[1-7], with [1-7] referring to a survey sweep (mcs1, mcs2, …, mcs7). Next, the file name gives information on the ‘focus’ of the information it contains. Below are the main file names, though individual sweeps may have some additional files. The star (*) in these file paths is used as a wildcard. We give a brief overview here, but explain the structures in more detail below, including discussing the variables required to identify observational units.
mcs[1-7]_family_*.dta- Contains family-level information (one row per family).
mcs[1-7]_cm_*.dta- Contains cohort member-level information (one row per cohort member). Some families have more than one cohort member (e.g., in cases of twins).
mcs[1-7]_parent_*.dta- Contains parent-level (or, more accurately, caregiver-level) information (one row per parent). Most families have two parents, but the number and identity of these parents can change between sweeps (e.g., in cases of divorce and remarrying).
mcs[1-7]_parent_cm_interview.dta- Contains cohort member-level information reported by individual parents (one row per cohort member x parent combination). A cohort member can be represented in two rows.
mcs[1-7]_hhgrid.dta- Contains information on the household grid (one row per member of the household).
mcs[1-7]_family_*.dta, mcs[1-7]_cm_*.dta, and mcs[1-7]_parent_*.dta are typically split across two files each, one for raw responses and one for derived variables (e.g., mcs1_cm_interview.dta and mcs1_cm_derived.dta). Note, mcs1_*_interview.dta does not mean the data was obtained via interview of the focal person themselves; for instance, a lot of the information in the mcs[1-7]_cm_interview.dta files is from parents.
mcs[1-7]_family_*.dta
Below is a schematic of the family-level files. There is one row per family and the family is uniquely identified by the variable MCSID. MCSID is a string variable that follows a standard but uninformative convention. The name of the variable is the same wherever it appears (i.e., it does not differ between sweeps). Below we show just three MCSIDs, which we’ll also use in the schematics for other data structures.
MCSID | … |
|---|---|
| M10001A | … |
| M10007B | … |
| M10005C | … |
| … | … |
mcs[1-7]_cm_*.dta
The cohort member-level files have one row per cohort member. Cohort members are identified with two variables, MCSID, the family ID, and [A-G]CNUM00, the ID of the cohort member within the family. The variable name for [A-G]CNUM00 differs between sweep, with the first letter referring to the sweep (ACNUM00 for the first sweep, BCNUM00 for the second sweep, …, GCNUM00 for the seventh sweep).1 While the variable name changes across sweeps, its value is persistent - a cohort member will have the same [A-G]CNUM00 value over time.
MCSID | [A-G]CNUM00 | … |
|---|---|---|
| M10001A | 1 (1st Cohort Member of the Family) | … |
| M10001A | 2 (2nd Cohort Member of the Family) | … |
| M10007B | 1 (1st Cohort Member of the Family) | … |
| M10005C | 1 (1st Cohort Member of the Family) | … |
| … | … | … |
On its own, [A-G]CNUM00 is not a unique identifier. Its value is 1, 2, or 3 for every cohort member. A singleton will be 1, a twin could be 1 or 2, and a triplet 1, 2, or 3.2 Both MCSID and [A-G]CNUM00 are required to uniquely identify a cohort member.
Because two variables are required to uniquely identify a cohort member (one of which is not consistently named across files), you may prefer to create your own single, unique identifier variable to make merging more straightforward. This can be achieved by concatenating MCSID and [A-G]CNUM00 variables (e.g., using the glue package [part of the tidyverse] in R; glue("{MCSID}_{[A-G]CNUM00}")).
mcs[1-7]_parent_*.dta
The parent files have a similar structure to the cohort member-level (mcs[1-7]_cm_*.dta) files: one row per parent. Individual parents are identified with two variables, MCSID and [A-G]PNUM00. [A-G]PNUM00 is the ID of the person within the family. Below we have records for two parents in the M10001A family. The first parent is number one, the second parent is number three.
MCSID | [A-G]PNUM00 | … |
|---|---|---|
| M10001A | 1 | … |
| M10001A | 3 | … |
| M10007B | 1 | … |
| M10007B | 2 | … |
| M10005C | 1 | … |
| … | … | … |
Like [A-G]CNUM00, [A-G]PNUM00 on its own is not a unique identifier. It lists the person number within the family, so it has to be combined with MCSID to identify a particular individual. Again, like [A-G]CNUM00, [A-G]PNUM00 has a sweep-specific prefix, but takes the same value across sweeps for a given individual (i.e., it is persistent).
The value of [A-G]PNUM00 is partly arbitrary. It does not specify a particular relationship to a cohort member. Such relationships are determined in the household grid files, which we discuss further below. The [A-G]PNUM00 does follow a convention, however. For non-cohort members, [A-G]PNUM00 is a positive integer between 1 and 99. For cohort members, [A-G]PNUM00 is equal to [A-G]CNUM00 multiplied by 100; i.e. for the first cohort member in a family it is 100, and for the second it is 200.3 While cohort members have a [A-G]PNUM00, non-cohort members (parents or other household members) do not get a [A-G]CNUM00.
Again, as two variables are required to uniquely identify a parent, you may prefer to create a single, unique identifier variable by concatenating MCSID and [A-G]PNUM00.
The mcs[1-7]_parent_*.dta files do not contain information only on (biological) parents. As people may enter and exit a cohort member’s household over time, the same individuals may not be interviewed each sweep. The study user guides can be consulted for further information on eligibility for the parent interview.
Note, Sweeps 2 and 3 also contain a mcs[2-3]_older_siblings_questionnaire.dta file. These files are structured similarly to mcs[1-7]_parent_*.dta - there is one row per sibling. Siblings are identified with MCSID and BHPNUM00 or MCSID and COPNUM00.
mcs[1-7]_parent_cm_interview.dta
The mcs[1-7]_parent_cm_interview.dta files record information from individual parents about individual cohort members, typically on the relationship between the two. For instance, in the first sweep, the file contains (among other data) information reported by each parent on whether they have ever lived apart from a particular cohort member.
As the MCS contains some twin and triplet families, each parent may report on multiple cohort members. As each parent may be interviewed, each child could be reported on by multiple parents. Below for the family M1001A, we have two parents ([A-G]PNUM00 1 and 3) who each report on two children ([A-G]CNUM00 1 and 2). Therefore, we have four rows for this family, one per parent x cohort member combination. For the other families, we have fewer rows, either because the family only contains one cohort member (as for the family M1007B) or the interview was only completed by one parent (as for the family M1005C).
MCSID | [A-G]PNUM00 | [A-G]CNUM00 | [A-G]ELIG00 | … |
|---|---|---|---|---|
| M10001A | 1 | 1 (1st Cohort Member of the Family) | 1 (Main Interview) | … |
| M10001A | 3 | 1 (1st Cohort Member of the Family) | 2 (Partner Interview) | … |
| M10001A | 1 | 2 (2nd Cohort Member of the Family) | 1 (Main Interview) | … |
| M10001A | 3 | 2 (2nd Cohort Member of the Family) | 2 (Partner Interview) | … |
| M10007B | 1 | 1 (1st Cohort Member of the Family) | 1 (Main Interview) | … |
| M10007B | 2 | 1 (1st Cohort Member of the Family) | 2 (Partner Interview) | … |
| M10005C | 1 | 1 (1st Cohort Member of the Family) | 1 (Main Interview) | … |
| … | … | … | … | … |
A helpful variable when using the mcs[1-7]_parent_cm_interview.dta file is [A-G]ELIG00. This records the type of interview the parent completed - either “1 [Main Interview]” or “2 [Partner Interview]”. The main interview (completed by the cohort members’ main caregiver) is longer than the partner interview. Accordingly, some variables in mcs[1-7]_parent_cm_interview.dta may only be reported by one parent. For instance, in Wave 1, birth weight was recorded from main interviews only.
Different people may answer the main or partner interviews over time - a parent may answer the main interview in one sweep and the partner interview in another, or a caregiver may leave the household and be replaced by another person. Therefore, while [A-G]ELIG00 can be used to merge data across sweeps (e.g., merge main parent interviews together), it is not a persistent identifier of a specific individual. [A-G]PNUM00 can be retained in this case so that individual respondents can still be identified post-merge.
Note, [A-G]ELIG00 also appears in the mcs[1-7]_parent_interview.dta files as the main parent interview also elicited additional information on the parent themselves.
mcs[1-7]_hhgrid.dta
The mcs[1-7]_hhgrid.dta files contain rosters of household members. There is a row for each individual (cohort member or not), regardless of whether they were eligible for, or participated in, an interview. Individuals are identified either with MCSID and [A-G]CNUM00 (cohort members) or MCSID and [A-G]PNUM00 (all individuals).
MCSID | [A-G]PNUM00 | [A-G]CNUM00 | … |
|---|---|---|---|
| M10001A | 1 | . | … |
| M10001A | 3 | . | … |
| M10001A | 4 | . | … |
| M10001A | 100 | 1 (1st Cohort Member of the Family) | … |
| M10001A | 200 | 2 (2nd Cohort Member of the Family) | … |
| M10007B | 1 | . | … |
| M10007B | 2 | . | … |
| M10007B | 100 | 1 (1st Cohort Member of the Family) | … |
| M10005C | 1 | . | … |
| M10005C | 100 | 1 (1st Cohort Member of the Family) | … |
| … | … | … | … |
The household grid files also contain a variable, [A-G]HCREL00, which contains the relationship of the person (ego) to the cohort member (alter) in their family (i.e., whether they are a natural parent and so on). Further, there are variables that define relationships between non-cohort members ([A-D]HPREL[A-Z]0 in mcs[1-4]_hhgrid.dta, EPREL0[A-Z]00 in mcs5_hhgrid.dta, and [F-G]HPREL0[A-Z] in mcs[6-7]_hhgrid.dta). The letter [A-Z] in the variable name maps directly to a [A-F]PNUM00: [A-D]HPRELA0 contains information on a person’s relationship to the person with [A-D]PNUM00 == 1, [A-D]HPRELB0 contains information on the relationship with [A-D]PNUM00 == 2, and so on. Given its complexity, the household grid files are described further in Working with the Household Grid.
Footnotes
-
The same letter prefix is also used for other variables from the same sweep, and (by and large) names for the same variable differ only by this letter between sweeps. (An exception is that names in Sweep 5, though beginning
E, differ from other sweeps.) For instance, in Sweeps 1-4, the name of the variable containing cohort members’ height areACHTM00,BCHTM00,CCHTM00andDCHTM00, respectively. ↩ -
Data from triplets is not available in the standard UKDS End User Licence datasets. ↩
-
Exceptions to this are
mcs[6-7]_hhgrid.dtawhere for all cohort members[F-G]PNUM00 == -1 [Not applicable]. ↩