The InterConnect consortium aimed to investigate the association between physical activity during pregnancy and neonatal anthropometric outcomes using a federated meta-analysis approach (Pastorino, 2018). The research question required the collection of meta-data from each participating study specifically relating to physical activity. For this exposure, information was collected for:
- The different dimensions of physical activity assessed
- Duration, frequency, and intensity of activities
- Type of work and employment status
- Information on commuting to and from work
Table P.4.1 summarises the physical activity domains that were assessed in the participating studies. Three studies had assessed household physical activity and four studies had asked about physical activity relating to travel mode. In contrast, all studies had assessed leisure-time physical activity and most had assessed work physical activity or at least had information on occupation type.
Table P.4.1 Physical activity domains that were assessed in the participating studies.
| Physical activity domain | Study 1 | Study 2 | Study 3 | Study 4 | Study 5 | Study 6 | Study 7 | Study 8 |
|---|---|---|---|---|---|---|---|---|
| Leisure-time | Y | Y | Y | Y | Y | Y | Y | Y |
| Work | (Y) | Y | Y | Y | Y | Y | Y | |
| Household | Y | Y | Y | |||||
| Travel | Y | Y | Y | Y |
Abbreviations: Y indicates the domain was assessed; (Y) indicates the domain was partially assessed.
After discussion, it was decided to focus on harmonising leisure-time physical activity since all studies had assessed this domain. In addition, leisure-time physical activity is important from a public health perspective since it is potentially more amenable to change than other physical activity domains. Within this physical activity domain, it was decided to create the following primary exposure target variables (Note: MET stands for metabolic equivalent of energy expenditure):
- Duration of leisure-time physical activity (hours per week)
- Leisure-time physical activity energy expenditure (MET.hours per week)
- Duration of moderate-vigorous physical activity (hours per week)
Study specific meta-data were reviewed in detail in order to establish which study could create which target variable. When necessary further clarifications on the methods used were sought from participating studies. Table P.4.2 shows the harmonisation potential across studies in the physical activity research exemplar.
Table P.4.2 Harmonisation potential across participating studies.
| Target exposure variable | Study 1 | Study 2 | Study 3 | Study 4 | Study 5 | Study 6 | Study 7 | Study 8 |
|---|---|---|---|---|---|---|---|---|
| Duration of LTPA | Y | Y | Y | Y | Y | Y | Y | N |
| Duration of MVPA | Y | Y | Y | Y | Y | Y | (Y) | Y |
| EE of LTPA | Y | Y | Y | Y | Y | Y | (Y) | (Y) |
Abbreviations: Leisure-time physical activity (LTPA); moderate to vigorous physical activity (MVPA); energy expenditure (EE), expressed in metabolic equivalent of energy expenditure (MET) per hour; Y = can be created; (Y) = can be created but with more assumptions and less precision; N = cannot be created.
Having defined the exposure target variables and assessed harmonisation potential, the next task was to create the processing rules to transform the variables from each study into the common target variable format. The processing rules were then explicitly agreed with each participating study. Examples of the available data from two studies and the algorithms or creation rules that were developed to derive each of the three above target variables are shown below in Figures P.4.3 and P.4.4.
Table P.4.3 Pre-existing data and algorithms used to derive three target variables for study A.
| Data available | Target variable | Units | Creation rule |
|---|---|---|---|
| Q1. How much do you do the following at present? • Jogging • Aerobic • Ante-natal exercises • Keep fit exercises • Yoga • Squash • Tennis/badminton • Swimming • Brisk walking • Weight training • Cycling • Other exercises Q1 units: >7h/w, 2-6h/w, <1h/w, never Q2. Nowadays, at least once a week do you engage in any regular activity like brisk walking, gardening, housework, jogging, cycling, etc. long enough to work up a sweat? Q2 units: hours/week |
Duration of leisure-time physical activity | Hours per week | Assign 7 h if >7 h/w, 4 if 2-6 h/w, 0.5 h if <1 h/w, 0 h if never.
Sum up hours/w for all activities |
| Duration of moderate-vigorous physical activity | Hours per week | Sum up hours/w for: Jogging, aerobic, keep fit, squash, tennis/badminton, swimming, brisk walking, weight training, cycling, other exercise. | |
| Leisure-time physical activity energy expenditure | MET.hours per week | Assign intensity (METs): Jogging=7; aerobic=6.5; ante-natal classes/yoga=2.5; keep fit ex=5.5; squash=12; tennis/badminton=5.7; swimming=6; brisk walking=3.8; weight training=3; cycling=6 |
For target variable 1, ranges from categorical data were recoded to single values; these were then summed.
For target variable 2, the duration data from target variable 1 were cross-checked with MET intensity data from the Compendium of Physical Activities. The duration of an activity was included in the total if its corresponding MET value was ≥3.0.
For target variable 3, the duration data from target variable 1 were combined with MET intensity data from Compendium of Physical Activities by multiplication to derive the estimated energy costs of each activity. These were then summed.
Abbreviations: LTPA: Leisure-time physical activity; MET: Metabolic equivalent task.
Table P.4.4 Pre-existing data and algorithms used to derive three target variables for study B.
| Data available | Target variable | Units | Creation rule |
|---|---|---|---|
| Q1. In your spare time did you:
A. Did you take walks for fun in the past week? B. Did you ride a bicycle in the past week? C. Did you play sports in the past week? (for example: tennis, handball, gymnastics, fitness, skating, and swimming) D. Did you do any other physical exercise in your spare time in the past week; for example, working in the garden and doing odd jobs around the house (do not include household activities). For each question: At what pace do you usually do this? • relaxed pace • average pace • brisk pace Q1 units: minutes per week |
Duration of leisure-time physical activity | Hours per week | Using Q1 A-C, convert minutes to hours. Add up hours of all activities (at any pace) |
| Duration of moderate-vigorous physical activity | Hours per week | Using Q1 A-C, sum up hours/w for: Walking at average or brisk pace, riding a bicycle at any pace, playing sport at any pace |
|
| Leisure-time physical activity energy expenditure | MET.hours per week | Assign intensity (METs): Walk relaxed pace=2.5; walk average pace=3.3; walk brisk pace=3.8; cycle relaxed pace=4; cycle at average pace=6; cycle at brisk pace=8; sport relaxed pace=3.8; sport average pace=5.5; sport brisk pace=7 |
For target variable 1, minutes of all activities were converted to hours; these were then summed.
For target variable 2, the duration data from target variable 1 were cross-checked with MET intensity data from the Compendium of Physical Activities. The duration of an activity was included in the total if its corresponding MET value was ≥3.0. Responses to question 4 were not included as intensity of activity could not be established.
For target variable 3, the duration data from target variable 1 were combined with MET intensity data from Compendium of Physical Activities by multiplication to derive the estimated energy costs of each activity. These were then summed.
Abbreviations: LTPA: Leisure-time physical activity; MET: Metabolic equivalent task.
