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. 2014 Jun;80(12):3708–3720. doi: 10.1128/AEM.00254-14

TABLE 6.

Daily normalized loads of pathogens and coliphages associated with final CART least-square regression tree analysisa

Microbial target CART data split criterion/criteria n Mean ± SD of terminal node microbial target data
Bacteria
    Campylobacter spp. (total MPN day−1 ha−1) Spring, summer 44 2.08 × 104 ± 4.12 × 104
Fall and UCTD 10 3.90 × 105 ± 3.52 × 105
Fall and CTD 8 1.09 × 106 ± 1.05 × 106
    Arcobacter spp. (total CFU day−1 ha−1) Fall, spring 71 2.92 × 106 ± 5.93 × 106
Summer 74 3.28 × 107 ± 1.38 × 108
Coliphages (total PFU day−1 ha−1)
    F-DNA Fall, spring 66 8.13 × 103 ± 3.59 × 104
Summer and UCTD 33 1.16 × 106 ± 3.02 × 106
Summer and CTD 38 4.12 × 106 ± 1.61 × 107
    F-RNA Fall, spring 66 3.62 × 105 ± 2.30 × 106
Summer and UCTD 33 6.71 × 105 ± 2.62 × 106
Summer and CTD 38 5.56 × 106 ± 3.23 × 107
    F-RNA GI (a/w animal) Fall, spring 66 8.94 × 104 ± 4.20 × 105
Summer and UCTD 33 2.81 × 105 ± 1.53 × 106
Summer and CTD 38 5.54 × 106 ± 3.23 × 107
    F-RNA GII (a/w human) CTD 73 1.31 × 104 ± 7.22 × 104
UCTD 64 4.81 × 105 ± 2.49 × 106
    F-RNA coliphage GIII (a/w human) No tree createdb
    F-RNA coliphage GIV (a/w animal) No tree createdc
a

Shown are the mean (arithmetic) daily normalized loads (and standard deviation [SD]) of pathogens and coliphages associated with final CART least-square regression tree analysis using as input drainage practice (CTD or UCTD) and season (spring, summer, or fall) as independent criteria. The results presented here are limited to the CTD intervention period (2007 to 2011) but include all available site data.

b

There were only 3 values above zero for this endpoint in this case, limiting the possibility of split combinations available for the program to test for group differences in microbial targets. After running CART on these data, CART lists the following as the classic output for this condition: “No useful split was found. No tree created.”

c

There were no nonzero data to apply splitting rules to in this case. (All data here were 0.) CART lists the following as the classic output for this condition after running the routine: “No learn sample variance for target.”