In this procedure one item block was created for each diagnosis and arranged next to each other with missing values recorded as responses from people with PD to the PAD specific item block, and vice verse.
Two traditional solutions to this problem are (i) either to remove the SNPs with the heterozygous signals from further analysis, or (ii) to code signals with the same P1 value as the A genotype, those with the same P2 value as the B, and those with a non-parental value, as missing values (recorded as "-") in a segregating population [ 26, 27].
In this approach, a model is posited for the association between missing values and recorded values, using records in which stage data are available.
Although the posted questionnaires captured self-reported outcomes, they did not capture physical assessments, and other missing values were recorded with the LVCF, which is consistent with an intention-to-treat analysis.
Thus, missing values in accident records can occur for at least two main reasons: eyewitnesses did not encode the sought-after information because they did not notice it, and/or eyewitnesses did encode the information (e.g., the absence of obvious clues) but did not report it [4].
Unfortunately, this non-random phasing-in of the participation requirements, together with inaccuracies and missing values in the recording of interview and agreement dates, makes identification of the impact of the reforms difficult for those in the grandfathered group with children already aged seven years or older as of 1st July 2007.
We also excluded 3184 (0.3%) records with missing values for time of birth, 334 (0.03%) records with unknown mode of delivery, 717 (0.1%) records where the deliveries were documented to have taken place in hospitals with fewer than 10 deliveries a year, and five records with inconsistent classification of perinatal death.
In the preprocessing process the duplicate records and records with missing values were removed.
When missing values occur because the records do not contain the sought-after information, researchers should first attempt to establish the meaning of missing values from external data whenever possible (e.g., from historical weather data, see Uttl et al. [15]).
*Sample size may vary due to missing values in the patient records.
