Table 1.
Descriptive Statistics, Phenotypic, Intraclass, and Cross-Twin, Cross-Trait Correlations
| Measured Variables | Grade | M (SD) | N | Min | Max | Skew | 1. | 2. | 3. | 4. | 1. | 2. | 3. | 4. | 5. |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1. LNF | K | 51.46 (17.31) | 1060 | 1.00 | 110.00 | 0.20 | 1 | .67**/.42** | .21** | .28** | .29** | .24** | |||
| 2. PSF | K | 39.81 (17.63) | 1227 | 0.00 | 85.00 | −0.44 | .43** | 1 | .26** | .50**/.34** | .14** | .15** | .07** | ||
| 3. NWF | 1 | 77.04 (36.23) | 1370 | 0.00 | 216.00 | 0.72 | .52** | .29** | 1 | .41** | .25** | .59**/.40** | .41** | .36** | |
| 4. ORF | 1 | 67.05 (35.64) | 1372 | 0.00 | 215.00 | 0.64 | .59** | .30** | .73** | 1 | .49** | .21** | .57** | .75**/.49** | .38** |
| 5. FCAT | 7 | 233.89 (22.14) | 1448 | 171.00 | 289.00 | 0.27 | .37** | .19** | .47** | .54** | .24** | .09** | .35** | .41** | .74**/.57** |
Note.
p<.0001,
M = mean, SD = standard deviation, N = number of twins, Min = minimum, Max = maximum, Skew = skewness. LNF = letter naming fluency, PSF = phoneme segmentation fluency, NWF = nonsense word fluency, ORF = oral reading fluency, FCAT = Florida Comprehensive Assessment Test - reading comprehension, K = kindergarten. Phenotypic correlations are presented in columns 8–11. Intraclass and cross-twin, cross-trait correlations are in columns 12–16. Intraclass correlations are on the diagonal; the first estimate is for MZ twins, the second for DZ twins. Cross-twin, cross-trait correlations are off the diagonal; the estimates for MZ twins are below the diagonal and for DZ twins above the diagonal.