What do small, vertical 'T' like lines at the top of bars on a graph indicate?

The small, vertical 'T' like lines at the top of bars on a graph are commonly known as error bars. They indicate the margin of error or the uncertainty associated with the data represented in the bars. Margins of error provide vital information about the reliability of the reported statistics, suggesting how much the actual values could vary from the sample mean. This visual representation allows viewers to assess the variability in the data and to understand the precision of the measurements.

In contrast, mean values typically represent a central tendency and would not be conveyed in this manner. Similarly, while ranges do indicate the extent of data, they are usually represented differently on graphs. Data points typically refer to the individual measurements or observations collected, rather than summaries like error bars. Therefore, the presence of these 'T' like lines effectively communicates the uncertainty and variability inherent in the data, making them a crucial element in interpreting scientific graphs accurately.