Life-cycle assessment data is often given in a table with one column for each product and one row for each stage. To interpret it, check the units, compare like with like, and find the total by adding the values for each stage. To compare products that are used a different number of times, divide the total by the number of uses.
Here is an example for the energy used by two bags. The plastic bag needs 3 MJ for raw materials and manufacture, 0.5 MJ for transport and 0.5 MJ for disposal. The total is 4 MJ. It can be used 4 times, so the energy per use is 4 ÷ 4 = 1 MJ.
The paper bag needs 4 MJ for raw materials and manufacture, 1 MJ for transport and 1 MJ for disposal. The total is 6 MJ. It is used once, so the energy per use is 6 MJ. The paper bag uses 6 times as much energy per use as the plastic bag.
Only energy was measured here. The data says nothing about pollution, water use or what happens to the bag after disposal, so we can only conclude about the impacts that were actually measured. A full decision needs all the impacts to be considered.