graphing: trendlines and outliers (anomalies)

shows points connected (NOT trendlines) suggests there’s a huge dip at 7 minutes this is probably NOT a true picture of the data! the OUTLIER point is probably an error. shows points connected (NOT trendlines) suggests there’s a huge dip at 7 minutes this is probably NOT a true picture of the data! the OUTLIER point is probably an error.

using trendline usually makes the overall trends clearer. the red trendline gives a better picture of the data than in the previous graph note there are different KINDS of trendlines most of the time, we’ll stick with LINEAR trendlines using trendline usually makes the overall trends clearer. the red trendline gives a better picture of the data than in the previous graph note there are different KINDS of trendlines most of the time, we’ll stick with LINEAR trendlines

this was the data table you were given. review your data carefully!

orange point is an OUTLIER a point that’s outside of the normal values NOTE IT IN YOUR LAB REPORT try to explain it put it in CONTEXT: this experiment is about pH values note: pH scale only GOES from 0-14!! it would be EXTREMELY ODD to have a change of -18! so this is likely a typo, or misread measurement in which case, it makes SENSE to see what the graph would look like without it

this red trendline shows what it would look like if the outlier were removed. but...

you can’t just eliminate data. you CAN look at whether it makes any sense. was it an error, or was it some real event? if error, what caused it? is it even POSSIBLE? if real, why so far off pattern? if it’s an error... how would things look if that point were absent?

this shows trendline if error is removed notice it SEEMS a much more reasonable fit this shows trendline if error is removed notice it SEEMS a much more reasonable fit

now focus on the GREEN (substance C) data...

here’s the same graph with the other lines removed for clarity shows a green linear trendline, AND the join-the-dots line how do the two compare? does the linear trendline show a reasonable picture of the data? here’s the same graph with the other lines removed for clarity shows a green linear trendline, AND the join-the-dots line how do the two compare? does the linear trendline show a reasonable picture of the data?

does the linear trendline seem to be a good fit? if NOT – SUGGEST ALTERNATIVES. SUGGEST WHAT THOSE ALTERNATIVES MIGHT MEAN. does the data level off? if so – why? does the data make a curve? if so, does that make sense? sigmoid curve? parabola? does the linear trendline seem to be a good fit? if NOT – SUGGEST ALTERNATIVES. SUGGEST WHAT THOSE ALTERNATIVES MIGHT MEAN. does the data level off? if so – why? does the data make a curve? if so, does that make sense? sigmoid curve? parabola?

maybe it’s a steep rise, and then it levels off... ? does this make sense? this would be a great place to do some background research. maybe it’s a steep rise, and then it levels off... ? does this make sense? this would be a great place to do some background research.

a linear LOBF ASSUMES that it’s a linear trend! but there are other trends... does your LOBF (trendline) actually represent what’s happening? a good lab report would show it both ways: (a) linear; (b) level-off then EXPLAIN which makes more SENSE under the circumstances