Second-Round-Harmonisation.md

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  | Do you recommend a specific tool to calculate the requested z-scores for harmonization of birth weights, heights etc as batch? | No. The z-scores only need to be harmonised if they already exist in your data set and/or if there are country-specific norms that are in general usage (e.g. both UK and France have specific growth curves that have been created for their populations). |
  | Our follow-up sweep covers a period of several years (i.e. different ages). How do we handle this given that the variables specify outcomes at specific ages? |  We suggest that you assume the follow-up occurred at the *average age* of the follow-up - so for 2-3 years, you could use 2.5 years, or for 11-15 years you could use 13 years. Alternatively, you could work out the average age of the children that were seen, e.g. for 11-15 year sweep it may be that the majority of children were seen at 11 years, but a small percentage were difficult to find and only followed-up later on; in this case 11 or maybe 12 years could be a more appropriate age to use. Remember, also, that there variables (in the 'child_vital_status' dictionary) where the exact age of the child at the follow-up should be recorded, so it will be possible for people to use this information if required. |
+ | Should we use chronological or corrected age? | Traditionally, correction for preterm birth was only carried out until 2 years of age, but this is starting to change. We recommend that you include whichever you have used for that particular follow-up sweep in the 'exact_age_dyrs_*' variables, and that you **make clear in the description of the data set whether data are based on chronological or corrected age.** |