Another group of 69 students in the same room was asked to guess the width in feet, to the nearest foot. The data in the Histogram Applet below is for the 44 student who guessed the length in meters. The histogram displays the values and the confidence interval is given in the bottom panel. The confidence interval is constructed assuming the data follow a normal distribution.
Normality justifies the use of the t-quantile in computing the upper and lower confidence limits.
The histogram shows that the data is positively skewed and possibly has outlying values. This is revealed more strongly by clicking on the Right Arrow Button two or more times to increase the number of bars and by selecting Add normal density from the Histogram Menu . The normal probability plot provides a more accurate assessment. Select normalPlot from the Histogram Menu and then select the Add quantile lines and Add robust fit menu items. The curve is concave upwards, which indicates positive skewness.