Note that the ordering of classes is somewhat arbitrary, such that different permutations of the same four classes can result from different starting values. In this analysis, it www.selleckchem.com/products/tofacitinib-cp-690550.html was apparent that the ordering of the classes was not consistent across the datasets (e.g., the nonsmoking classes might be the first class for some imputed datasets and the second class for others), consequently we chose to carry out the LCA on each dataset in turn and pool the results ourselves. Regression Modeling of Risk Factors To examine the relationship between risk factors and our latent classes, a two-stage modeling procedure was used. Following the LCA, class assignment probabilities were exported to in Stata version 11-MP2 (StataCorp., 2009).

These probabilities were incorporated as an importance weighting (iweight) in a series of univariable multinomial logistic regression models. For the imputed data, the 100 imputed datasets were re-stacked and analyzed using by Stata��s mi routines. Results Characteristics of Participants The starting sample for these analyses is the 13,973 singletons/twins who survived at least until 1 year of age. Of these, 3,038 respondents provided complete data on the three measures (1,245/41% boys and 1,793/59% girls). A further 2,232 missed one response and 2,052 missed two responses, resulting in a dataset of 7,322 with at least one of the three measures (3,351/46% boys and 3,971/54% girls). First, the relationship between level of response (complete/partial/none) and baseline demographics was studied.

There was evidence of an association between level of response and gender as well as housing tenure, parity, and maternal education with complete responders being more likely to be female, have parents who own their own home, have a mother educated beyond high school, and have fewer siblings (data available on request). Level of response was also related to smoking frequency. Table 1 shows the relationship between smoking frequency at each time point and whether the respondent provided complete or partial smoking information. There is strong evidence that those who provide partial smoking information are more likely to smoke regularly. Table 1. Relationship Between Smoking Frequency and Degree of Response Latent Class Analyses Nonimputed Data For the latent class model, there were 64 possible patterns of response.

Of these, 46 were observed in the complete case dataset of 3,038 participants. This sample was dominated by a nonsmoking GSK-3 pattern (none/none/none), which was the response for a total of 2,339 (77%) respondents. There was little evidence of regular smoking before the age of 15, with other common response patterns being none/none/occasional (n = 151, 5.0%), none/occasional/none (85, 2.8%), and none/none/weekly (52, 1.7%). The partially missing dataset contained an additional 57 response patterns.