In addition, the manual completion of telephone response forms resulted in a substantial amount of missing data, as first and second-tier EOC staff often overlooked key data elements in their efforts to provide timely responses to public demands.
To estimate bias due to missing data, we first tested whether the missing data were missing completely at random by applying a user-written routine for Stata, ~mcartest~.
The dependent variable was missing data at first follow-up, and in the analysis we adjusted for age, sex, trial, and severity of condition at baseline.
Both when UPHIs, names and addresses or when only demographic details are used as linkage variables, the degree of missing data must first be quantified and its impact reduced by creating linkage algorithms that allow for missing data.
In order to impute missing data, we first calculated the full samples' mean cortisol change between the time point with the missing value and the adjacent time point; for all time points except awakening, we used the time point prior to the missing value.
Where there was missing data, a second analysis was performed used multiple imputation with 20 copies of the dataset and using a regression approach for imputation.
Open image in new window Fig. 3 Plot that visualizes missing data for Data source 3. Data Cleaning First, we identified the data columns where data are frequently missing.
Namely, the population size in the first example was 150, but due to missing data in the first eight sets, the average size per marker pair was 56; in the second example, the sample size for the first eight sets was 50 and no missing data were simulated.
The closest weather station was given preference as the source of weather data for a particular PTC site and the data from the second one were used to fill in for the missing data from the first station.
We applied a Last Observation Carried Forward (LOCF) strategy for missing data after the first round that is to say that, if an expert did not answer the second round, we considered his answers at the first round.
