Accumulation of wear and tear in archival and library collections. Part II: an epidemiological study

Heritage Science

Table 3 Results of t-tests and descriptive statistics on the percentage of failed sheets within an inventory number grouped by the type of protective enclosures, (A) including all observations and (B) including only inventory numbers containing more than 100 sheets

Exposure variable	Outcome variable: failed sheets (%)			n	95% CI for mean difference	t	df	p
Exposure variable	M	SD	SE	n	95% CI for mean difference	t	df	p
(A) Portfolio	21.9	21.2	2.2	94	− 8.6, 6.8	− 0.24	155	0.812
Box	22.9	30.2	3.2	88	− 8.6, 6.8	− 0.24	155	0.812
(B) Portfolio (> 100 sheets)	25.2	17.1	2.5	46	1.3, 15.5	2.37	88	0.020
Box (> 100 sheets)	17.7	16.8	2.5	45	1.3, 15.5	2.37	88	0.020

M, mean; SD, standard deviation; SE, standard error of the mean; n, number of observations; CI, confidence interval; t, t test; df, degrees of freedom; p, p-value