TABLE 2.

Description of dimensions that comprise each level with example student text and justification provided by coder.

	Level 1	Level 2	Level 3	Level 4
Argument structure	Tautological/simple	Additive/one-sided	Relational/two-sided	Compound/conditional
Example text [coder justification]	The results above conform to the hypothesis that as the efficiency of DNA repair mechanisms increases the mutation rate decreases. [Known difference in DNA repair used to explain known difference in mutation rate]	Combining the data from Part I and II, it can be deduced that the E938 strain’s status as mut− [high mutating] allows it to better survive. [Makes claim about success of high mutator only]	Overall, since there are so many things that affect the reproduction of bacteria, such as when a mutation occurs, what kind of mutation occurs, and human error, it is difficult to use our limited data to determine which strain would be more suited for survival. However, the general trends of our data suggest that having a high mutation rate is beneficial to survival. [Makes claim about success of high mutator, but only after relating to other possible claims]	It might seem like a good idea to argue against DNA repair. However, due to the staggeringly small percentage of the population that develops beneficial mutations, it does not make evolutionary sense to argue this point. [Considers advantages of high and low mutators and reconciles using evolutionary argument]

Scope of knowledge/evidence	Relies on given information and/or unspecified results	Uses subset of available data as evidence to support inference	Relates data that show different patterns	Relates data and brings up outside information or hypotheticals/ thought experiments
Example text [coder justification]	Our results showed that E938 (Mut−) was more likely to mutate than E939 (Mut+). [Mentions “results” without explanation or elaboration. Facts about mutation rates given.]	In Part I and II E938 was able to grow more colonies on plates containing an antibiotic and in Part II E938 was able to adapt to using lactose as a food source. [Combines two parts of data to support claim with some explanation, ignores agar data]	The lower mutation rate … does not allow it to mutate enough to generate a significant number of bacteria that could digest lactose, … On another note, both bacterial strains survived roughly equally as well in the environment with just LB Agar. [Considers data from all environments]	Together these data provide support for the hypothesis that an increased mutation rate was beneficial to bacterial survival. …. While more mutations appear to be an advantage, the relationship between mutation rates and repair mechanisms remains intriguing. If these results hold true in nature, then why is DNA repair so pervasive? Statistically, with more mutations comes a higher chance for an organism to mutate in a non-beneficial manner as well. [Considers consistency between data and patterns in nature including statistical hypothetical argument]

Consistency and closure	Closed without rationale, ignores inconsistencies	Closed with some rationale, ignores inconsistencies	Closed, addresses inconsistencies	Appropriately qualified or open-ended
Example text [coder justification]	The results of both parts of the experiment conformed to what was expected. [Concludes with certainty due to match to expectations]	This observed pattern was consistent with what was seen in the lab class [as] a whole, indicating that the results of this study are reproducible. [Uses reproducibility to justify certainty, but does not address other inconsistencies]	Overall more mutations can be beneficial for a species as a whole given that there is a higher possibility that the species will be able to adapt to changing environmental factors; however given more mutations there is a higher possibility that individuals will not be able to survive in a given environment. Essentially, a higher rate of mutation adds to the genetic diversity in a species, which has been proven to be an important factor in a species ability to survive [Addresses possibility that mutations are not beneficial, yet still concludes with general claim about advantage]	While this experiment successfully displays the advantages of a high mutation rate in an unfamiliar environment, the similar lawns of bacteria that appeared on the LB plates limit our ability to determine the effects of mutation in a non-hostile or unfamiliar environment. [Explores possibility of different outcomes in different contexts]