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diff --git a/Documentation/mobile-manual-v3.txt b/Documentation/mobile-manual-v3.txt index 77e877eeb..d68008be4 100644 --- a/Documentation/mobile-manual-v3.txt +++ b/Documentation/mobile-manual-v3.txt @@ -2,8 +2,8 @@ // Subsurface-mobile User Manual // ============================= // :author: Manual authors: Willem Ferguson, Dirk Hohndel -// :revnumber: 3.0.0 -// :revdate: March 2020 +// :revnumber: 3.1.3 +// :revdate: February 2021 :icons: :toc: :toc-placement: manual @@ -18,7 +18,7 @@ image::mobile-images/Banner.jpg["Banner",align="center"] // toc::[] -[blue]#_Version 3.0.5, May 2020_# +[blue]#_Version 3.1.3, February 2021_# toc::[] @@ -261,6 +261,7 @@ to open a map with the dive site in an integrated map viewer. This of course is only possible if the dive site is associated with GPS information. +[[S_Filter]] === Filter the dive list By default, all the dives in the dive log are shown in the dive list. After several years your dive @@ -491,7 +492,226 @@ The summary page lists the date of your first dive in the dive list as well as y It also provides two columns of data for selectable time ranges (by default all dives in the dive list and the dives during the last six months. -=== Export + +[[S_Stats]] +== Dive Statistics + +[width="100%", frame="None"] +|=== +a|image::mobile-images/StatsPanel.jpg["Image: Statistics panel",float="left"] | + +Creating meaningful statistics that convey the information you are looking for is surprisingly hard. +Different users have very different needs and very different expectations. Subsurface-Mobile provides +a rather detailed set of statistics features to summarise information from the dive log in a graphical +way. To access the dive statistics tool, select _Main Menu_ -> _Statistics_. The statistics tool is +so flexible that it is impossible to cover every possible use case. Rather, we provide a conceptual +introduction, followed by specific examples. The tool can be closed using the _Back_ button (bottom +right in Android). + +The Statistics tool has two panels (image on left): + +1. A setup panel containing comboboxes for requesting a graph (top). + +2. The graph that has been requested (bottom). + +|=== + + +[[S_Stats_Intro]] +**** +*A diver's introduction to statistical graphs* +[icon="images/icons/important.png"] +[IMPORTANT] + +The extreme flexibility of the Statistics tool means that you need to provide detailed information about +what information Subsurface should provide. It helps to have a clear objective, i.e. a solid understanding of +what you want Subsurface to show you. In other words, you need to formulate the correct question. There +are so many graphical display options that, if you do not formulate the question correctly, the information +is unlikely to be presented in a valid or appropriate way. Because all statistical results in Subsurface +are shown as graphs, formulating an appropriate specification requires four steps: + +a) Which dives do you wish to graph? If required, use the xref:S_Filter[Filter button] for selecting specific dives to be analysed. + +b) Which variable should be displayed along the bottom horizontal axis of the graph? +Let's say you wish to see how many dives you performed each year. In this case the variable along the bottom +horizontal axis would be "Year". Alternatively, if you wished to compare the mean depth of your dives using +different suit types, then "Suit type" would be selected as the variable for the bottom horizontal axis. +Alternatively, if you wished to visualise the water temperature for dives of different dive depths, +then you would select "Max. depth" as the variable on the horizontal axis (see image below). The variable +along the horizontal axis is also called the "base variable", the "X-axis variable" or the "independent +variable": it defines the basic units or categories used for analysis. + +image::mobile-images/StatsGraphAxes.jpg["Example: Statistics graph axes",align="center"] + +c) Which variable should be displayed along the left-hand vertical axis of the graph? This is the variable +that you are primarily interested in. In some cases this could just be a count such as "No. of dives". +However, if you are interested in water temperature at different dive depths, you would select "Water +temperature" as the variable along the vertical axis (see image above). In this case you are primarily +interested in water temperature, not in dive depth (which would be the variable along the horizontal +axis). The variable along the vertical axis is also called the "data variable" or the "dependent variable": +it is the variable affected by (or dependent on) the values of the variable along the horizontal axis, as +in the graph above. + +*NB:* Since, in Subsurface-Mobile, the graphs can be rotated to be horizontally-oriented or vertically oriented, +the terms "horizontal axis variable" and "vertical axis variable" are not appropriate. We use the term *Base +variable* to denote the conventional horizontal axis variable and the *Data variable* to denote the conventional +vertical axis variable. + +d) Which chart type do you require? By default Subsurface selects the most appropriate graph type, but this +is a user-selectable option. Taking the example of water temperature at various depths above, the image below +shows three of the possible chart types of the same data: Image A shows the raw data by plotting the exact +temperature and depth for each dive. Image B, however, groups the dives in 5m depth intervals within which the +temperature for each dive is indicated (the red marks are explained below). Image C also groups the dives in 5m +depth intervals. However, in this case the minimum, maximum, mean, upper quartile and lower quartile are shown +for each depth class. + +image::mobile-images/StatsGraphOptions.jpg["Statistics graph options",align="center"] + +The point of the discussion above is to show that, _before initiating a graph, you need to think carefully +about what you want Subsurface to show_, at least keeping the above four aspects in consideration. + +*A more technical note on the valid use of statistical graphs* + +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 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. It is easy to determine whether a specific graph is a barchart or a histogram: +when selecting "Chart type" the heading of the submenu should show either _Barchart_ or _Categorical_ +in the case of categorical variables, and _histogram_ or _scattergraph_ in the case of continuous variables. +Subsurface-Mobile helps by showing a yellow triangle for graph types likely to be inappropriate (Image C). + +image::mobile-images/StatsDataTypes.jpg["Statistics: bar-charts of continuous and categorical data types",align="center"] + +**** + +=== Graph orientation + +In many cases the values of the Base Variable along the horizontal axis are shown by dots, not numbers or names (Image B above). +This is because the screen of a mobile device often is not wide enough to show all the values, especially prevalent +in bar charts where the labels along the bottom axis are long. There are two ways of addressing this problem: + + +1. Turn the mobile device through 90 degrees so that the screen display is in landscape (wide) mode. + + +2. Rotate the bar chart through 90 degrees by selecting a horizontal bar chart (in the +Chart type combobox, select a horizontal chart type). In this case the bars are shown horizontally in both portrait and landscape orientation. For instance, +the image below shows the horizontal bar-chart produced when selecting "Categorical/Horizontal" in the Chart type combobox and +using the same dataset as in graph B in the image above. With the axes rotated there is much more horizontal space for showing +the relatively long label for each bar in the chart. + +image::mobile-images/StatsBarchartRotated.jpg["Stats rotated barchart",align="center"] + +=== Graphs of counts data + +By default, when the Statistics panel is opened, a histogram is shown of the number of dives performed each year. +This is an example of *counts* data. To request a graph representing counts, three comboboxes need to be set: + +a) The top left combobox of the Base variable needs to be specified. Which variable should be along the horizontal + axis? Examples are Year, Buddy, Rating, Max. depth. + +b) The binning combobox (top right) for the Base variable needs to be specified. This represents the increment +for each bar along the horizontal axis. For instance, when counts of number of dives are extracted for years, +this could be in increments of a year, a quarter (3 month period) or a month. For some variables, e.g. Buddy +or Rating, a binning value is not relevant and cannot be selected. However, for others, e.g. Year or Max. +depth, selecting the appropriate binning is important. + +c) For simple counts data, the left combobox of the Data variable needs to be set to "none". This is because +a data variable is not involved in this type of graph. Divers used to spreadsheets may prefer a *pie chart* +for these data, achieved by selecting "piechart" from the Chart type combobox. It is possible to +simultaneously provide counts for two variables. In this case one could specify a Data variable which +results in the counts being subdivided according to the data variable. This option does not have a piechart +equivalent. + +For simple histograms, the default height of each bar is determined by the mean value for the observations +included in each bar. However, this can be manipulated using the Operation combobox to show the mean, +maximum, minimum, median and sum applicable to each bar. Image A below shows quarterly count data of +dives while image B shows quarterly count data, subdivided by dive mode (some dives open circuit, +other dives rebreather). The legend can be dragged around so that it does not obscure part of the graph. + +image::mobile-images/StatsCountsData.jpg["Counts data example",align="center"] + +=== Counts comprising more than one category in a bar + +As mentioned in the section above, bar-charts showing a breakdown of each category for a number of +subcategories are easily created. + +a) Select a variable with categories (along the horizontal axis) as a Base variable (e.g. dive mode or suite type). + +b) Select another category of data as a Data variable (e.g. gas type or cylinder type). + +The images below show two alternative bar-chart representations. If, in the Chart type combobox, one selects +"Barchart/stacked vertical", a graph similar to image A below is generated, summarising a log of technical +dives where, for each cylinder gas type, the bar is subdivided into a count for open-circuit dives and for +rebreather dives. On the other hand, if "Barchart/grouped horizontal" is selected in the Chart type combobox, a graph +similar to image B, below, is produced. Here the subdivision within each gas type is shown as adjacent bars. + +image::mobile-images/StatsBarchartSubdivided.jpg["Stats subdivided barchart",align="center"] + +=== Scattergraphs + +[width="100%", frame="None"] +|======= +a|image::mobile-images/StatsRegression.jpg["Regression data example",align="center"] | +Sometimes you might wish to investigate the relationship between two dive variables. Has my SAC rate decreased over +the years? Is the water temperature colder at greater dive depth? One of the ways of investigating these questions +is to draw a scattergraph where the values of one variable is plotted against the other variable (see image on the left). + + +For the dataset in the image on the left the SAC rate appears to have decreased over time. If the relationship between the two variables +is statistically significant, a red line is shown that summarises the best estimate of the relationship between SAC rate and year. +In this graph it appears that SAC rate has decreased from around 21 l/min to around 14 l/min between 2013 and 2021. The pink area +around the red line indicates the uncertainty of the precise orientation of the line. The line is expected to lie somewhere within +the pink area with a certainty of 95%. The intensity of the pink colour also indicates the relative reliability of these estimates. +The procedure for obtaining a scattergrapth is: + +a) Specify the Base variable: Which variable should be along the horizontal axis? Examples are Date, Temperature, Max. depth, SAC rate. + +b) Set the binning value for the Base variable (top right) to "none". + +c) Specify the Data variable: Which variable should be along the vertical axis? + +|======= + +=== Comparisons between categories of dives + +You might wish to compare different categories of dives. Is the (5-star) Rating of a dive related to water temperature? +Is my SAC rate related to diving with different dive suits? Since dive suit and Rating are categories, a scattergraph is not +appropriate. The default is a categorical dot graph, which, in the case of image A below, shows the precise water temperatures +for each Rating. The red lines indicate the top quartile, the mean and the lower quartile of temperature for each rating. The +column with no star indicates dives for which a Rating has not been selected. It appears that dives with a 5-star rating have +higher temperatures than the other ratings. To obtain a categorical graph: + +a) Select a variable with categories (along the horizontal axis) as a Base variable (Top left). + +b) Select the data variable and set binning to "none" (middle right combobox). + +c) By default the Chart type combobox shows "Categorical/data points". If this is not the case, select this value. + +image::mobile-images/StatsCategoricalData.jpg["Stats: Comparison of categories",align="center"] + +Alternatively you could create a Box-whisker graph for the same data. In the Chart type combobox, select Categorical/"box-whisker". +This creates a graph indicating the maximum, top quartile (Q3), median, bottom quartile (Q1) and minimum for each category or +class. Image B above shows a box-whisker graph for the same data as image A above. You can see that the values for a Rating +of 5 stars tend to be higher than for other ratings. + + +== Export The _Export_ feature is somewhat experimental. On Android it only allows the upload of your dive list to two websites (_divelogs.de_ and _diveshare_). On iOS it also allows local file based exports as _Subsurface_ |