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| -rw-r--r-- | Documentation/user-manual.txt | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/Documentation/user-manual.txt b/Documentation/user-manual.txt index ae1575428..4fba29ee3 100644 --- a/Documentation/user-manual.txt +++ b/Documentation/user-manual.txt @@ -2821,7 +2821,7 @@ The point of the discussion above is to show that, _before initiating a graph, o When graphing variables from a dive log, there is an important distinction between _continuous variables_ and _categorical variables_. These two data types are typically graphed in different ways. A continuous variable can theoretically have any value. For instance dive depth can have any value greater than zero (theoretically negative depths indicate height above the water but this is not a practical possibility). Consequently, depths of 21.63857 meters or 44.7653 feet are entirely realistic. Dates are also continuous since the annual value of any particular instant in time can be presented. For instance a dive at 12 noon on April 1st 2020 can be presented by a value of 2020.24726 (90.5/366 days in that leap year). On the other hand dive mode is a categorical variable: there are no values between "Freedive" and "Open circuit" or between "Open Circuit" and "CCR". Other categorical variables include Buddy, Visibility, Rating and Suit type. Different methods are used to represent these two types of variables, evident from the way in which the axes are organised. It is perfectly valid to create a graph with a continuous Base variable and a categorical Data variable and _vice versa_. However, when using a continuous Base variable, use a -histogram, NOT a bar-chart. The images below show counts of dives at different depths. Image A is a histogram showing that no dives were conducted between 55m and 60m depth. However two dives were performed between 60m and 65m: these two bars (55-60m and 60-65m) have equally important information. Image B shows the bar-chart of the same dataset where depth has been converted to a depth type. Notice that the two bars with no dives (55-60m and 75-80m) are omitted. Important information is lost because of the use of a bar-chart to represent continuous data. +histogram, NOT a bar-chart. The images below show counts of dives at different depths. Image A is a histogram showing that no dives were conducted between 55m and 60m depth. However two dives were performed between 60m and 65m: these two bars (55-60m and 60-65m) have equally important information. Image B shows the bar-chart of the same dataset where depth has been converted to a categorical type. Notice that the two bars with no dives (55-60m and 75-80m) are omitted. Important information is lost because of the use of a bar-chart to represent continuous data. image::images/StatsDataTypes.jpg["Statistics: bar-charts of continuous and categorical data types",align="center"] |