3. Results1) The mean and standard

3. Results
1) The mean and standard deviation scores with the performance of the
PR and the FT groups at 10, 22 and 30 months of age in the IDHC measures
are shown in Table 2. Table 2 also shows the results of the comparisons
between the PR and the FT groups (t test). The t tests carried out
indicate that there were no significant differences between the
two groups in any of the IDHC measures taken at any age.
In relation to the norms of the IDHC [36,37], the mean raw scores obtained
by the PR and the FT groups in all the IDHC sections at 10, 22 or
30 months of age are well within the normal variation, and correspond
to percentile scores between 25 and 75, and most of them were around
percentile 50.
When the children were sorted into more subtle GA groups, the
descriptive results they obtained are given in Table 3 for 10, 22 and
30 months of age. This table also shows the results of the one way
ANOVA performed to compare the results of the different GA groups.
As can be observed, the results obtained by the 4 GA groups were very
similar, and no significant difference was observed in any case.
The results obtained for cognitive development and quality of home
environment (measured at 22 months of age), two of the predictive
variables introduced in the regression models, were the following for
the PR and the FT groups. The mean total score (and SD) in the Batelle
scale for the FT group was 260.00 (22.28), and for the PR group was
245.96 (21.63). The t test mean comparison indicates that FT children
obtained significantly higher scores than the PR children (t (179) =
−3.69, p = .001). The mean raw scores obtained by the PR and the FT
groups were, however, within the standard deviation for the Spanish
normative sample of the Batelle inventory of the corresponding
age (M = 247.29, SD = 23.57), and correspond to percentile 50
(IQ = 100) and percentile 70 (IQ = 108), respectively [39]. The mean
(and SD) total score in the HOME scale for the FT group was 38.70
(3.97), and for the PR group was 38.23 (4.32). There was no significant
difference between groups (t = −.625, p = .533). The mean results
obtained by the two groups in the Home scale fit in the fourth
quartile, indicating relatively good quality of the children's environments
[41].
To check the possible effect of cognitive development on the results
obtained in the former ANOVAs,we introduced the Batelle total score as
covariable in a series of ANCOVAs where the independent variable was
the GA of the four groups, and the dependent variables were the results
obtained in the different measurements of the IDHC. The results
paralleled those obtained before with the ANOVAs, indicating that the
effect of the independent variable remains unchanged. Therefore,
although there were relationships which reached significance between
the covariable and the dependent variables, these do not affect the
relationship between the independent variable (GA groups) and the
dependent variables (scores obtained in the IDHC measures).
2) Finally, different hierarchical regression analyses were performed in
order to identify the factors which predict linguistic development. As
commented on above, a series of variables were taken as predictive
factors for the regression analysis.
The first hierarchical regression analyses aimed to obtain those factors
predictive of word production, usually considered a good measure
of language development, at 10, 22 and 30 months of age.
The results obtained are shown in Table 4 for each age. The most
important results indicate that word understanding and gestures and
actions at 10 months are good predictors of language production at
10 months, and even at 22 months of age. In the first case Model 1 predicts
25.4% of variance of word production at 10 months, and 7.6% at
22 months of age. The inclusion of other variables in Model 2 hardly
increments the variance explained (3.4% at 10 months and 4.2% at
22 months of age).
However neither word comprehension nor gestures and actions
seem to predict the results obtained in word production at 30 months
of age, and the introduction of the other variables in Model 2 does not
change this fact. No other variable had a significant predictive effect.
Given that neither gestures nor word comprehension has any significant
effect on language measures at 30 months, the effects of other
variables were tested in subsequent hierarchical regression analyses.
In the search for predictors of language scores at 30 months of age,
new regression analyses were performed. First, cognitive development
measured at 22 months of age through the Batelle scale and vocabulary
production at this same age measured with the IDHC were entered in

Model 1. As Table 5 shows (upper part), nearly 40% of variance of word
production at 30 months of age was explained by these variables.When
maternal education, stay in NICU, gender, HOME total score and
gestational age were added (Model 2) the variance explained for word
production at 30 months